Lately I can be outside in Central London with 4 or more bars showing on my HTC Desire but can't make or receive any calls. This happened in the Putney area last week and yesterday I was in Camden so I thought it must be a network problem until my mate with an Orange iPhone sat next to me and starting making calls with no problem. Anyone else finding this? The phone says its dialing on the display but seconds later it says call ended. I do try various different numbers just to check but get the same results. Cheers.