Okay I have seen so many of these questions and I decided to make a guide. This one will be based off that for a Mac as I believe more Mac users have iTouch/iPhone than PC.
Update: The procedure should work for PC aswell. I added a link to an SSH program from PC.
In order to get any ROM's onto a iPhone you will need a number of things.
-Game Bios
-ROM's
-Open SSH
-Fugu or any other SSH program
..::Game Bios::..
Game Bios is very easy to get. I am not sure if I am allowed to post then though. It is very simple to find, a simple Google is the key.
..::Roms::..
Also very easy to find, Google is your friend.
..::Open SSH::..
To get open SSH on your iPhone there are many ways you can get it but I will tell you the way I thought was the easiest. Assuming that you have jailbroken your iPhone, go to installer and download the following:
-OpenSSH
-BSD Subsystems
-Ulctl
From there turn on SSH which is easy after that and make sure that your iPhone and computer are going off the same wifi router.
..::Fugu::..
Download fugu if you are on a Mac (http://www.versiontracker.com/dyn/moreinfo/macosx/15693). From there we will connect your iPhone to Fugu.
Update: For PC download this Winscp: (http://winscp.net/eng/download.php).
If it does not work tell me.
-Go to your iPhone and click Settings>General>Auto Lock>Never. Then go back to settings and click Wifi>(Blue Arrow on your Connection).
-On your Mac, copy the ip Address into the Connect To. For the Username change it to Root. When it connects(it can take a sec) the password is alpine.
edit: If you are still on firmware 1.0.2 first off I recommend upgrading to 1.1.1 but if you choose not to the password is dottie.
..::Placing ROMs::..
-Place all roms in a folder named GBA. Then create another folder named ROMs(Cap sensitive) and place GBA inside it.
-Now on Fugu go to Applications>gpsPhone. In there place the bios from before.
-With the ROMs folder, now go back to Fugu and place it in Var>Root>Media and drag and drop it anywhere in there.
Update: For 1.1.3 and Up place files in Var>Mobile>Media instead
Now you should be able to play your ROMs! I hope this helped as I have seen too many threads about this and not many in depth guides.