That is a fundamentally broken design. There is literally no excuse for a simple messenger app to suck up a gigabyte daily. How do you expect people to adopt this when they have broadband and wireless plans with data caps?
I know nothing about TOX design, but it makes (to me, at least) some privacy sense to saturate the network with noise that is in message length, their interarrival time and recipient characteristics similar to the actual communication. No idea if TOX does that.
