Unfortunately I think it's one of those situations where the existing tech is "good enough" and there is not profit incentive to make it better. There is an incentive to amass a large user base (with associated network graph) so you can achieve a high valuation, but there is no incentive to create a new messaging protocol that can sit on top of the cell network.

If anything, this is a task for non-profit orgs like the IEEE, IETF, EFF, etc. to be working on and funding.