Until mobile customers in these places gain access to a real internet connection they'll be locked into whatever their mobile providers allow. The moment they can do an SSL protected request to a website with their phones (or even better, send arbitrary protocol data to arbitrary IP addresses) that will all change. For now, they could theoretically use a dial-in telephone banking style interface like BitcoinIVR or something similar but that may be cumbersome and burn precious minutes to use it while also requiring them to trust the IVR operator.

They need internet access to really be able to use bitcoin. I dont think thats really possible on the <$20 phones these people can currently afford.