Unfortunately, many cell phones these days, like the HD2 will come loaded with what is called a SIM lock. This is something that basically prevents you from using another carriers service or data plan to save money. If you try to stick in any SIM card other then your original carrier, the phone will probably only work for 911 calls and the likes. Luckily this can be fixed in only a few minutes!
Once you have an unlock code for your HTC HD2 mobile phone, you are ready to begin the unlocking instructions. You can find the original steps this article is based on here. Here they are:
Unlock a HTC HD2 phone
1. Power on your HTC phone with an unaccepted SIM card in (or no SIM card at all).
2. Enter your HTC unlock code you acquired earlier.
3. Your HTC phone should be unlocked and may automatically reboot
Also just in case you were wondering the HTC HD2 is also known by some carriers as the HTC HD2 T8585 or HTC Leo 100. Essentially they are all the same smart phone.
In fact, you can try calling up your mobile phone carrier’s support line and requesting one since you will be foreign.(ex : T-Mobile) to open the lock key and the will inform you the unlock key. Otherwise you can try searching Google for some HTC unlocking software or generators
By the way, below the flow of requesting unlock key from provider unlock.