No Sim Message (in Vietnam) Need a Fix, Calling All TechHeroS, I NEED U!!!

[SiCo]

Hi Folks, Like I said in the title, I'm in Vietnam which I don't know if that's relevant but I thought I'd mention it , and I've got this little beauty of an iPhone 4 and I keep getting the 'No Sim" message, despite having my Mobifone (one of the big carrier co's over here) sim inside. I've tried the on/off Airplane thing, no joy, and a couple of other things but it's not hap'nin and despair's starting to creep into my usually hopeful (some would say hopeless!) outlook. Could it be that I need to let the carrier, Mobifone, know that I've changed from a 'normal'/regular GSM phone to an iPhone?? I don't know about these things, and getting info from Mobifone isn't easy but if someone who knows what they're talking about tells me I need to contact them obviously I will. I'll do anything!!! Legal, of course, OK, semi-legal, I'm not a choir-boy!! No offense to any choir-boys, especially any that can fix an iPhone 4!!! PLEASE HELP, don't make a grown man grovel, and beg, no-one wants to see that, do they?? If you know someone who might be able to help then please tell me how to go about making contact. OK, I'm in your hands people, be gentle with me, it's my first time.