Update: It's been a long time since this post first came out, so long that Rwandatel doesn't even exist anymore and Airtel is the new carrier in town. A few of these codes still work, but if you are in East Africa in general and have an Android device, download SimBuddy from the Play Store for an easy way to get access to all these shortcuts.
Since I'm always playing with all three carriers either for data access or to test something I figured I'd put up a quick cheat sheet for the various carriers.
MTN
- check balance: *110#
- add credit: *111*[code]#
- apn: internet.mtn
- buying internet bundle (1000 MB): *345*1000#
- checking bundle: *345#
Tigo
- check balance: *131#
- add credit: *130*[code]#
- apn: web.tigo.rw
Rwandatel
- check balance: *221#
- add credit: *220*[code]#
- apn: rtel3g
- username: rwandatel
- password: rwandatel
- auth type: chap