I'm curious if you could implement a GSM/3G phone using software defined radio, using a device such as BladeRF/USRP. Amittedly they're not small enough to use

I'm curious if you could implement a GSM/3G phone using software defined radio, using a device such as BladeRF/USRP. Amittedly they're not small enough to use as a normal phone though. Maybe you'd be able to scale down that tech though one day?