The word is still out on Verizon's GSM radio functionality. Seems its crippled in some way and wont give the same experience as the AT&T model. For e.g., GSM will likely not work in the USA because the whole idea of these CDMA world phones is to provide the option for limited GSM use while traveling, but locked only to the CDMA network at other times. Many have tried unsuccessfully to fully unlock GSM in the US.
If you already have Verizon service then go for it, but I wont recommend switching to Verizon for the Pre 3 and the idea of a 'world phone.' Its not even clear weather the Vodaphone SIM can be swapped for another in the UK or elsewhere (the last time I checked) so GSM use while traveling is questionable. W/ respect to network options, speeds and service costs you may fare better w/ an unlocked AT&T model both within and without the US.
I have a UK qwerty Pre3, an AT&T as well as Verizon.
I bought the UK one first, as I didn't think the others were coming out and thought I could just use it on AT&T back in the States. Then the AT&T one started showing up on ebay, so I got that because I wanted the faster faux 4G. I came from Sprint where I had a pre- then frankenpre2, but was extremely disappointed with the reception of the AT&T network in my area (work and home - both around Hollywood), so I took the plunge a 3rd time and got the Verizon pre3.
For me, even if the data network isn't as good (ie, 3g only) the normal coverage absolutely craps over AT&T. If the world phone doesn't work, not a big deal as I have the other ones and can just throw in a local sim for them.
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