nokia n900 doesnt support at&t 3g
nexus theirs rumors it will others say it wont.
the thing people dont understand nokia n900 its more of a internet tablet you get a full internet experience but their alot of things lacking still and in the works. its a great device full flash support, linux so its pretty hackable maybe more than android in the future.
nexus has a super fast processor a more mature android a better touch screen but still lack full on web experience.
my money would go to nokia im a nokia fan even if im using htc right now they seem to have more experience in their belt. google seems to me like they want to follow apples foot steps and they just trying to bring out the next big iphone killer and they kinda forgot about g1,mytouch,and even the motocliq seems to be down and under and google doesnt seem to care much about old devices lets not talk about rogers magic and dream stuck to 1.5 donut nothing else.
