Today the NTT DoCoMo network — as well as all the W-CDMA networks in the world — use the standard version of UMTS, allowing potential global roaming.
from
http://www.answers.com/topic/umts
Also known as UMTS (Universal Mobile Telecommunications System), WCDMA (Wideband CDMA) is the 3G standard chosen by most GSM/GPRS wireless network operators wanting to evolve their systems to 3G network technology. WCDMA offers enhanced voice and data capacity and peak data rates faster than most dial-up services and average rates consistently greater than GSM/GPRS (Global System for Mobile communications/General Packet Radio Service) and EDGE (Enhanced Data for GSM Evolution). As of February 2006, more than 51 million subscribers were using WCDMA for their mobile voice and data needs.
from http://www.3gtoday.com/wps/portal/!ut/p/kcxml/04_Sj9SPykssy0xPLMnMz0vM0Y_QjzKLN463dAHJmMUbxBub6k eiijjCBbz1fT3yc1P1A_QLckMjyh0VFQHj6obn/delta/base64xml/L3dJdyEvUUd3QndNQSEvNElVRS82XzNfOUU!?page=home
japan uses UMTS
playing safe doesn't always lead to success dude. they could have adapted 3g or hsdpa into their iphones and later adapt the "standards" into their 2nd gen iphones if they like. speaking of universal standards, i don't think such thing will happen. what can possibly happen is interoperability of these existing standards.
take note also that the standard widely accepted by the user will not be the factor, but the standard widely being used by operating networks around the world will be the common denominator. and apparently it's UMTS...