I have been using an unlocked E71 on AT&T since I purchased it at a Best Buy on Nov 2008. I have the 450 minute plan for $39.95 with the $29.99 smartphone unlimited (all data) add-on. They do not offer this anymore. I originally selected it after I purchased the HTC Star Tek (Cingular 3125) Windows smartphone through AT&T back in 2005.

I finally broke down and purchased an N900 the last day of August 2010 . I have wanted it since I learned about it in 2009 and had been following and reading this site frequently. What kept me from purchasing it was the fact that the N900 would only use the 2.5 G frequency band on AT&T. My E71 uses both 3 G and 3.5 G all the time and is suprisingly fast.

I decided to try Simple Mobile (uses T-Mobile) unlimited and so far the N900 has been fast on 3G when out and about. At home, I usually use my High Speed Internet via my WiFi.

So I continue to use my E71 on AT&T and my N900 is currently on the $60.00 Simple Mobile plan for almost three weeks now. I have not yet reached there phantom data cap. The battery on the N900 would probably die out if you used data excessively unless you plan to always be tethered to a wall socket, such as when using the N900 as a laptop replacement.

All in all, I like both of my phones and plans so far (for my needs). So it depends on your ultimate satisfaction and concessions. I do not believe that there is a freely available $20.00 unlimited data offering anymore, from what I have read, most carriers are trying to split up there data offerings using different pricing levels for more revenue.

Good Luck ! Sorry for the long post.