GSM not working on three network

Hi
i am trying to use the GSM shield with a three sim card, i have successfully used the same shield with an o2 sim.
Im using the "TestGPRS" sketch from the examples, it cant seem to connect to the network.
It gets stuck on "Connecting GSM network..."

I know i have signal cause i have used it with my ipone that is in the same place as the device.

Thanks

Three is 3g only.
They have no GSM 2g coverage - your GSM shield doesn't work on 3g frequency.

Martin.

Thank you