I have exactly the same problem. I'm on Vodafone UK and my number is unknown too. I rang the customer suppport line and they said they cannot do anything about it, and they told me to ring HTC support. HTC also said they can't help. All the people that work in support centres are foreign, and they don't seem to understand what you are saying, it's so frustrating! Furthermore, I used to have a Nokia N96 with the same sim card, and when I upgraded the guy said he had updated my sim to work with the HTC desire. I think it's a sim card problem, so I may get it replaced. I also wanted to use an app, is it Tikl you speak of? I'm gutted it don't work, it's supposed to be rad. My friends all use it and say it's hilarious, you can walkie talkie loads of friends at the same time. It's frustrating that this has happened to some of us
The phone identity and HTC sync are two things that can't be resolved and it's so annoying.