[Serious] How much bandwidth does it take to send a transaction to the network?

If mainstream adoption should take place, then transactions should take a minimal amount of bandwidth to interact with the network. Both for smart contracts and for the average transaction.

If the average Joe was out of luck and became homeless, they would have a hard time having a reliable internet connection. Some cell phone providers allow an unlimited 2G bandwidth connection (~128 kbps) with those without a (or expired / used up) prepaid data bucket. In this case, would the average Joe be able to reliably interact with the Ethereum network with this amount of bandwidth?