If you want the benefits of GSM (which are many), IMO AT-n-T is not the way to go right now. VoiceStream is the only carrier that has a more-or-less nationwide network you can use all over the country. Cingular will let you roam onto VoiceStream's network when you're out of their GSM service area, but I don't see any reason to choose them over VS. They are typically more expensive, though this varies by market, their network in CA and NV is overloaded to the point of prompting a class-action suit, and their customer service is only open WEEKDAYS.
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1. With the T68, I wouldn't be able to use the phone on AT&T's non-GSM network which has much broader coverage. Is that right?
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That is right. ATT is selling a Siemens Frankenstein phone with TDMA and GSM in the same handset that will let you use GSM when it's available and TDMA when it isn't. This unit is not a good compromise in terms of features or performance. ATT will *not* let you roam onto Cingular or VoiceStream at this time.
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2. If I manage to get an unlocked T68, are there other networks in the U.S. that I could use without signing up for some other plan? Could I just get some prepaid or similar plan from someone else?
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You can use a prepaid SIM from either VoiceStream or Cingular. Or get an international "roaming" SIM from any one of a number of carriers. But why? Unless you are getting ATT for free or have to keep your existing number, there is little to recommend them. Their network is almost non-existant, voice rate plans uncompetitive, and high-speed data freakishly overpriced at $10/MB.
If you want a T68, go buy it from VoiceStream for $249, sign up for a plan you like, and start enjoying the features and voice quality of GSM. Their coverage in Chicago is generally very good. Activate international roaming and use it almost anywhere in the world just like you were at home with rates about 70% lower than ATT or Cingular.
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3. My understanding is that in Europe, I could fairly easily do what I'm describing in (2). Is that right?
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Europe and the US are the same in this regard, except in some European countries you would have more choices of carrier.
It sounds like I am pushing VS, I think. I'm not. Usenet has a long and rich history of my rants against them. But from a service/company perspective they are no better or worse than any of the other US carriers, and from a network/technology perspective they simply have a better product.
-alan in seattle