In Australia this is how you used to top-up prepaid phones with a credit card or check your balance. You can probably still use SIM applications to do it now but it seems to be mostly replaced by web portals.

Yeah. Telstra prepaid still do the phone driven menu, where you "call" a number, but instead of voice a text menu pops up on your phone. It's quite nice actually. I think they're called USSD menus?

USSD is correct! http://en.wikipedia.org/wiki/Unstructured_Supplementary_Serv...

Same for Tanzania, Uganda, Rwanda, and I suspect a lot of the rest of the (non-Eastern) Africa.

USSD codes are critical.

Tanzania? Not so sure. What I've seen in Dar is that the way to access mobile money for instance is to dial 150XX# to access services. SIM Toolkit Applications on the contrary present as regular phone applications (albeit limited by the SIM tooklit capabilities).