UMTS GloballyUMTS is the first global wireless standard, J-Phone in Japan, which uses W-CDMA access technology can interface with UMTS, in contrast, the current GSM networks are available everywhere except Japan and Korea.
NTT DoCoMo’s network, the UMTS alternative for 3G, FOMA, also uses WCDMA. FOMA is incompatible with UMTS directly, but the relationship between FOMA, UMTS, NTT DoCoMo and AT&T is such that this situation has the possibility to turn into global roaming. NTT DoCoMo holds an 18% share in AT&T wireless; they also held a share of 20% in 3UK. These foreign interests will pave the way for global roaming possibilities.
All UMTS/GSM dual-mode phones should accept existing GSM SIM cards. Sometimes, you are allowed to roam on UMTS networks using GSM SIM cards from the same provider.