As we all know we can roam on T-mobile. But can we now use T-mobile sim cards in or Orange phones?

Mine was an upgrade from Orange, since left them but the PAYG options are awful.

Well it worked. I can call etc from my orange phone using t-mobile but no internet

Was told I'd have to buy a rolling sim only deal from t-mobile after 3 months. Not a huge wait I guess. Just so happy that phones locked to Orange(like my iPhone4) can now take t-mobile sims

You'll need to add the APN settings for the network you want to use.

Connecting the handset to iTunes with the T-Mobile SIM in should force through a Carrier Bundle update which will solve your issue.

If not, you MAY be able to goto Settings-General-Network-Cellular Data Network and add the relevant settings there. You can find these by searching for T-Mobile iPhone APN Settings on the net.

One issue you might have is when using an Orange SIM the Cellular Data option is removed as park of the Orange carrier bundle. This should default to the T-Mobile option but as i've never tried to I don't know what that is.

3G is now working and active on an Orange locked iPhone4 using a tmobile sim