Not sure if this helps at all, but I am a Telus Mike customer and I travel to the states a lot. I have been coast to coast and my phone seems to behave the same.
My 7520 works fine for the most part on Nextel's network, roaming is automatic and seamless.
Phone, DC, email, Google Maps, html/wap browser and Blackberry Messenger work without any problems.
Veri-Chat and Mobile SSH (BIG problem for me) do not work at all though. Nothing I have tried works.
For me the data roaming charge is $8/MB (CAD) and I usually charge up about $4-$6/CAD on a 4 day trip. I try to keep my usage to a minimal, I am sure most of the charge is from using Google Maps. I do receive about 100 emails a day on my Blackberry though.