You have to understand AT&T is the second largest provider in the US @ 78 million subscribers. For apple starting out; going with AT&T or Verizon was the best options. Go with one of the two largest vendors.

TMO is only @ 33 million.
Verizon is @ 88 Million
Even Sprint has more US customers than TMO.

If you add several of the CDMA subscribers together you have a 170 million between a handful of providers. Making a single CDMA version of the phone could unlock a huge market in the USA for Nokia. Adding AT&T bands could unlock another 80 million subscribers. So if your Nokia, would you settle for only targeting a maximum potenial of 11% of the market or going for like 100% of the market by just adding two additional versions of the phone. Even if they decided to blow off AT&T (because of the iphone penetration on AT&T) and just add CDMA they would at be targeting 73% of the USA market...

Nathan