If you know what a phone with both GSM and CDMA can do then I guess you’re happy. If you don’t then you should: it allows you to travel from CDMA networks, like those in the States to other countries (or AT&T/T-mobile) where you need GSM. This is what the new Motorola RIZR Z6c can do.
Motorola already sent the RIZR Z6c to FCC for approval and from what I’ve heard so far it features EV-DO rev. 0 so which makes me think it will probably head to Verizon or Sprint? A phone that can be used worldwide no matter what plan you have is becoming more and more popular (see the new BlackBerry 8830) so I guess Motorola want to be amongst the first to have it.