There are three main genre's of mobile games: retro games, modern single-player games, and MMO games.  I believe that the future of mobile gaming is the retro game, because a lot of people who have access to a smartphone can relive their childhood through old system emulators.  Modern single-player games always have the chance to do what Tetris did and become their own franchise, but that's a very hard mark to hit.  MMO games may pick up more players over time, but their complexity lends itself to larger screens.  A MMO game that utilized the cellphone's size as part of the game would be a hit, versus mobile ports of popular MMO games such as today's big MMORPG's (WoW, Everquest, etc). 

Making a game out of a tool may become popular; I think of games such as a taxi tracking game using real world maps and the phone interface as potential hits.

Finding a mobile game is easy : in France at least you can open any newspaper that is more or less about technology, gamin or even just the TV news and you'll get a few ad pages about logos, ringtones and games. If you missed those, you cna still catch up with the TV-ads showing some low-end games. Those games are usually low-budget and not that good. 

If you want to get serious about mobile gaming, the way to go is to go on your operator's mobile portal where you have a wide selection of the latest EA games, Gameloft and more mobile games and where you usually can get demo version for free for a dry run. That's where experienced mobile gamers usually head to, it's the one stop shop to discover, test and buy new games. But this approach is really limited to advanced users as getting on the operator's mobile portal and navigating to the desired section still remains a pretty tough job for most of the end users around here (I had the perfect example with a co-worker of mine trying to buy a ringtone - was a painful experience).

The last place you find cool games are online on video games websites that now all have a dedicated mobile games section where they review the latest killer games. In that place you're almost sure to find high-budget mobile games with some good movie licences (marvell heroes...). If you're really an addict, you can even go directly to the top mobile games makers' website (EA and gameloft) where you can discover their latest releases.

Mobile Game Downloads Have a Promising Future

There are many sources for finding and downloading mobile games online. However, I'm most excited about what the next year or so will hold as mobile gaming expands from small phones to the iPhone and other smartphone devices. Larger screens, improved hardware, touch-screen capabilities and improved software development kits promise a more sophisitcated gaming experience for mobile users.

Game Stores, Aggregators, and Communities

Myxer:
http://www.myxertones.com/

ugenGames:
http://www.ugengames.com/

CNET Gamespot Mobile:
http://www.gamespot.com/mobile/

GameJump:
http://games.gamejump.com

HOVR:
http://www.hovr.com

ispott:
http://www.ispott.com/

SendMe:
http://www.sendmemobile.com/

MultiGames:
http://www.multiga mes.com/

Search Engines and other resources for finding Mobile Games and cheats

GameSkoot:
http://www.gameskoot.com

Providers and Innovators

Here's where things get really cool...

Apple iPhone / iPod Appstore:
http://developer.apple.com/iphone/program/

XLR8:
http://www.xlr8mobile.com

Adobe Open Screen Project:
http://www.adobe.com/openscreenproject/

Since I've had mostly smartphones as my main phone for the past decade, I have a wider range of choice than most consumers with feature phones. My storefront of choice has usually been Handango. They have a wide variety of options, sorted and ranked, the reviews are useful, and I have a wallet stored there. That said, prices for PDA/Smartphone games have always been on the high side, say ~$15 where from a carrier's deck there usually is a cheaper option - albeit a subscription.

Handmark is another site that I have used, but I have moved off them since I find their content very limited, and they are always trying to push their "Pocket Express" application, which is essentially a subscription service for those people who are too lazy or stupid to bookmark a few free mobile sites that do the same job.

I have bought content for some feature phones that I owned from the carrier's deck. Both J2ME and BREW fit into this category. The experience was simple, and easily billed. The downside is that it's hard to find the content, and it's expensive if you keep it for many months.

I have downloaded free and paid games directly from a developer's website on occasion, although this is less frequent. The problem here is that the websites and developers are often very obscure. These companies have a hard time getting the word out of their existence, and their marketing budget usually is not adequate for a big ad campaign. Thus, my experience here is the exception rather than the rule. More often, I'd get the developers games off an aggregator like Handango.

I have bought smartphone games at retail stores and Amazon.com as CDs. Often there are multiple games on a CD gamepak designed for PalmOS, Windows, etc. I think I bought games from Astraware this way.

On my N95, I have not paid for any games, but Nokia has several (confusingly arranged) different portals, download stores, free stores, and such in the embedded links in the phone, as well as the dedicated N95 companion website. I have downloaded free Symbian games to the phone from these sources. Nokia's main problem, as they push OVI, is to start making sense of all their efforts: Club Nokia, Ovi, Preminet, Forum Nokia, the embedded download links, the companion website... it feels like a maze of content, like the author Borges' "Biblioteca de Babel".

As for what phone platforms have the best games, who knows? Every platform has its challenges and idiosyncrasies for developers. Feature phones, by and large, are just too weak. With so few MIPS, they can't do much. Smartphones can do better since they have more horsepower, and larger screens. In that camp, the PalmOS is weak since it doesn't have multi-threading, the Windows Mobile OSes are OK, and the Symbian OS can be pretty good. One of the most powerful phones for processing and video hardware is actually the iPhone, but its closed environment and lack of hardware buttons limits its gaming ability. I'd single-out the N95 as a darned good platform, since it has good sales numbers, good screen, landscape ability, lots of hardware buttons, large memory, and a good processor and video capability.

As for input methods, I prefer good hardware buttons, although accelerometer devices are also cool. I've seen some good prototypes using the camera to sense motion, and replicate the accelerometer functionality. I like hardware buttons for game use that are NOT close to other functions, for example, on most smartphones I've used, I'll be in the middle of a game, and next thing I know, I've activated my calendar.

At the MWC, I saw a neat start-up Zeemote (http://zeemote.com/) that had a bluetooth joystick for playing with phone-based games. It was pretty cool. It was held in the hand and had a thumb-operated top-hat control and a trigger finger...um...trigger. I got the chance to demo a helicopter shooter game on an SE device, and it was pretty cool. That solves my problem of dropping into my Calendar by hitting the wrong  button! Their problem, at first, will be getting enough games to work with the Zeemote. But it definitely addresses the input issue dead-on.

MMORPGs? Not my thing. I'm retro. I play 80s video games on the phone because of my age, and because of the time slices I have available, and because these games have UIs, complexity, and resolution needs that almost perfectly match the phones. Galaga, PacMan, whatever, I have Atari game paks, and a bunch more. I like these and I like newer puzzle type games. I think that the power of the phones will quickly surpass this generation of games, but that they will still have staying power, because of the demographics, and because no matter how much resolution the phone screens can do, and no matter how many 3D triangles a phone can draw, many phone screens will continue to be 2", which has "Asteroids" written all over it.

I've never picked a phone based on a game, and to this point I think very few have. This may change in the future as mobile versions of popular MMORPGs get mobilized well. But for now, mobile phone gameplay is mostly in the domain of filling in time on a phone you would otherwise be carrying. Serious mobile gamers have dedicated devices. Nokia, clearly, aims to change this, but has had limited success thus far. In reality, it is very difficult to make a good mobile phone that is also a great game device: too many compromises are required of each split personality, and the end device finds it difficult to compete with dedicated products.

Mobile Games Genres and Where to Find New Mobile Games

1) Sports and Leisure Sports Games:  These games involve simple simulations of popular sports and leisure sports.  Games include baseball, golf, football, basketball, hockey, soccer, racing games such as Nascar  (though racing games are sometimes considered a separate genre) and even fishing.   In fact EA's most popular title in leisure sports category is the ESPN Bassmaster fishing simulation followed by Sims bowling and pool.  Very popular sports games are Tiger Woods Golf, NBA Basketball, and Madden Football.

Look for new sports games at these links:
Electronic Arts Sports
Electronic Arts Leisure Sports

2) Casino Games and Card Games  are often gambling simulations of real casino games.    Texas Holdem, slots, and (non gambling) solitaire are very popular now.  Casino suites of games such as roulette and slots and blackjack are also mainstays of this genre.

http://www.888.com/mobile/
http://casino.ladbrokes.com/en/mobile/games

3) Parlor Games:  An age-old game genre, Chess, checkers, backgammon and many other parlor games are available for mobile.   When buying this type of game look for suites of games that include several that you'll want to play.

4) Sim Games:  Role playing is increasingly popular in all online spaces and mobile Sim games are as diverse as the mobile version of the popular Sims PC game to Grey's Anatomy to Goodfellas to Adult themes.   Generally expect mobile play to be a lot more restrictive than the PC or console versions of these games.  This genre may also cross over with Action Games and Mobile MMORPGs. 

5) Action, Adventure, Strategy Games.   From Harry Potter to Doom to the Simpsons. Action games from first person shooter games to role playing strategy games abound. These tend to be stronger on console or PC applications than mobile platforms, but there are many mobile attempts.  Even titles like Grand Theft Auto often have a mobile version, though the game play on the mobile versions is generally nothing like PC or Console versions. 

6) Word. Logic, and Puzzle Games.  Games such as scrabble and hangman, word games are well suited to the mobile environment because they often require less screen space and usually require concentration more than playing actions that are restricted by the mobile hardware.    Puzzlers like Soduku or Tetris are also popular.   EA puts their SIMS games in this genre but I'm not clear why.

7) Arcade Game Classics:  These are generally the old arcade games that ushered in the new era of video games seveal decades ago.  Asteroids and PacMan to name a few.
http://www.mobilerated.com/arcade-mobile-phone-games.html

8) Massively Multiplayer Online Role Playing Games.   Look for this genre to become very interesting in the near future as Blizzard enters the fray.    An excellent blog review of Mobile MMORPG games is here.  He seems to feel that Shadow of Legend is a great game where TibiaME is also worth trying out.

More Games Sources:
Electronic Arts
real.playp.biz
Microsoft UK
gamespot.com
gameloft.com
vgmobile.com
shockwave.com

Also, look for Blizzard to develop some exciting Mobile Games soon.

Caution!   There are unscrupulous mobile application vendors who offer "free" services buried in deceptive cell phone contracts that are often hard to cancel.   Read the fine print and use caution whenever downloading any mobile phone software - free or otherwise.