Thanks for the extremely detailed replies J-Hop2o6 and Viper Matrix Wireless. I think I mostly understood everything.
A couple points for clarification:
1) When I was asking if coverage for 1900 Mhz HSPA+ would be just as good as AWS, when the refarm is done, I meant in terms of geographical area covered (numbers of towers, I suppose?), not technically how good is the building penetration (although that's a nice plus to know about). Will I get coverage in all the same places that I might go with my AWS phone right now, with a phone that does HSPA+ on 1900 Mhz?
2) Is there a way if I can tell right now if I'm getting HSPA+ on 1900 Mhz, without have a 1900 Mhz HSPA+ phone (I have a Nexus One)?
3) Viper when you say that it would be best to get a phone that has the 850/1900 bands, are you saying that this will be preferable to a phone with AWS HSPA+? That is, if it's a choice between one or the other, since there are very few phones that have both.
4) Eventually will this mean that AT&T phones are completely compatible with T-Mobile's network both on HSPA+ and LTE (using AWS)? They would work just as well as a T-Mobile phone?
Thanks again for all the details and explanation above.
There will be more towers to provide coverage on 1900 than AWS 1700. I wasn't trying to speak about building penetration. I was comparing on the coverage you get over GSM 1900 today is comparable to what you'd receive over HSPA+ 1900.
Depends on the Nexus One version you own and if the software supports switching over to WCDMA 1900 or Band II. Looks for the Nexus One your either or have 1900 or just 1700. If you have AWS HSPA+ then you won't have PCS HSPA+.
850 will be featured in newer phones and this is just for AT&T roaming. Phones after the Sensation support 1900 HSPA+. It is better to have both AWS HSPA+ & 1900 HSPA+ than to have just one but 1900 HSPA+ would serve better. Phones on T-Mobile will support both.
AT&T phones in the future will support LTE on AWS LTE but AWS HSPA+ on T-Mobile will eventually be moved completely on PCS HSPA+ completely. Making AWS HSPA+ convert over to AWS LTE completely. But AT&T hasn't made a HSPA+ 42 phone just up to 21. Since AT&T really only has 14.4 deployed mostly. It would discontinue AWS HSPA+. AT&T doesn't have plans so far to have HSPA on AWS. 1 of the phones I pointed out is a first for AT&T LTE Roaming on T-Mobile. So 700 Band 17 could be seen in more phones as well.