hmmm...owned them both
I have owned both phones. Go to the Blackberry website and compare the 8900 and the 9700. Same dimensions, SAME camera, same screen. THE phone are sooo close in build and the OS is PRETTY much the same.
ONLY differences is the 9700 has: 3G, slightly better keyboard, and the track pad...oh...OS 5.0 too but you REALLY can't tell the difference between them unless you REALLY look for little stuff. 5.0 will be out soon for the 8900 as an over the air upgrade anyway.
If you can get the 8900 for free with contract or something: it is a solid phone. Also, I wouldn't buy a new blackberry with anything less than 256meg of base memory though. Only the Tour, 8900 and 9700 come with 256 meg. Oddly, the Bold 9000 had 128 meg (too bad for it).
IF both phones are for the same price? The 9700 has the extras! But you should pull a 8900 for $0-$99 with contract (cheaper). I also SWEAR my 8900 had a better batter life than my 9700 although the website claims different....