Ringtones for Phones

I’m going to taiwan in around 2 more weeks, and I’m planning to bring my g1 back to taiwan. The problem is that I don’t want to use the sim card from america~ which I want to get a pre paid sim card from 7-11 in taiwan, so do u guys know if it will work if I just but the prepaid sim card in my phone?? Which my phone is unlocked already~ answer quick~ since if its not going to work, I will have to get another cell phone soon!! Thx