Hello, I am facing a strange problem. Today I purchased an unlocked Hero. I have to different SIM cards from different service providers. I installed the first one and worked w/o any problem. Later on, I tried the other provider's SIM and on the screen it says No Service. Sometimes, I see the reception bars but cannot make and receive any calls. What may be the reason ? I assume that there is no problem with the hardware as it is working with one of my SIM cards. TIA..