Eat, Ride, Sleep, Repeat!
Well Sir, I have seen few phones in US available with Global warranty. Its a new concept and is only available with higher end phone. So it might not be available in your case. Have to find a deal for it online. The unlocking can be done on a CDMA phone to use a GSM SIM on it. I have not tried it personally but my friends have done unlocking on Samsung Galaxy series and IPhone. It was quite successful, but still risks are involved. You can easily find local mobile shops with banner "Mobile Unlocking". These guys specialize in unlocking CDMA phones/Dongle into GSM ones. Here is a link with more info on unlocking:There will not be any warranty any ways since I'll buy that phone in US. What do you mean by unlock the CDMA phone?
Again, risks are involved. Your phone might never work again. So do it at your own risk.