All that is left is spoofing the servers with openbts for when this calls home to on the pi clusters then we have our own cellular service to play with.
the Ofcom position on this matter is available for review at http://stakeholders.ofcom.org.uk/consultations/gsm_gateways Where it states clearly that any commercial use remains illegal and could include prosecution under the Wireless Telegraphy Act.
Whilst this means that an organisation using SIM cards in a gateway for its own use is not necessarily illegal
Thus the requirements seems to still comes down to no charge access, private usage only within a 30 meters radius of transmission and a 6 dBi antenna. Sure 802.11 base stations get better than that but hey why not play around with the tech just to learn?
'ell if we where this tight arsed about 802.11 back in the 90’s then everyone would still be on dial up or something more crappy.