What network was the phone on originally?

Three UK are very good at blocking phones that have been listed or that they deem to be suspicious.

I had a three contract phone and when the contract had come to term they told me to keep the phone. Then they blocked it! So i used generic firmware and was able to access all other networks except three.

You could always ring them up and ask them to unblock the three network to your phone, they will need your imei and sim card number.

When you turn your phone on it broadcasts your imei number etc to your sim provider who then allow coverage to your phone. If your imei number isnt accepted its simple, it gets blocked.

Plus their could be other reasons like your sims only a 2G sim and not a 3G sim. Three started to block quite alot of 2G sims sometime ago in a bid to get everyone to go onto 3G Sim cards. Of course this wasnt very customer friendly as there are still quiet alot of 2G handsets out there that simply will not accept a 3G sim.

Hope this helps

Lavondys