ROIP - Radio Over Internet Protocol ..... If the owners of GiifGaff, Telephonica made a service like Zello, but left only for customers of GiffGaff, O2 and other firms owned by the Spanish giant, possibly Tesco Mobile who are 50% owned by O2, this would give those that want it instant push to talk communications.
It is all set up working on an app on the handset's 3G or 4G service, and it's like a 2 way radio system that people set up as their own.
You could have 2 to 100 or more with there own network.
Push to talk is instant to those in the users own network
have a look at www.zello.com for a look at a similar idea