I had an interesting experience today as I had to replace a lost SIM card and lo and behold nothing worked as before as far as data was concerned. On calling T-Mobile I was asked what phone I had and told them an N900 and then they told me that I HAD to upgrade to the $29.99 package. I argued of course that I had a $19.99 unlimited text and internet package before and so why didn't this work now? They told me that I had no choice. Having read the posts here and elsewhere all I had to do was change the internet settings and hey presto, it works again! So thanks for posting all your experience as without you guys I would be $10 poorer per month from this time onwards!!

Has any one switched over to an android phone, from the n900, and been able to keep your $10 plan?

Yes I have, I went from Nokia N900 to HTC Incredible S to Nokia N9.

No problems. Just don't call them.

I believe that you can keep your plan, if you switch to certain unlocked/unbranded android devices (there are a few that support the AWS band T-mo USA uses for 3G). Otherwise (switching to T-mobile branded devices, for example), it's typically not possible.

For the most part, you can't use T-Mobile branded Android phones and keep the $10 plan, but there are a few exceptions out there that'll work (the HTC Panache and the Galaxy Nexus for example). Nothing is guaranteed to work forever though obviously.

There are a ton of other phones sporting other OSes that will work as well. HowardForums has a fairly comprehensive (though not a complete) list of phones that are compatible that you can check out. The column headers are pretty self explanatory except for the SIC (Strength of Internet Compatibility) one--you generally want a 3 (works with no modifications) or 2 (works with minimal modifications) for that column.

Additionally, if you aren't already aware, T-Mobile is starting to refarm their 1900 spectrum which should make unlocked AT&T branded phones work on T-Mobile web2go plans with full speed sometime within the next year or two.

I got the Google Nexus S International Version (i9023) a couple of days ago--it's been working with my $5 web2go data plan on epc (no need to switch it to internet2). It's slightly larger than a n900 but has the same number of pixels so density isn't as good, but it's actually a good size as it's big enough for reading without being obscenely large like the Galaxy II, Nexus, and Note. The international version is generally considered a downgrade from the US versions (i9020) as it uses a "super clear lcd" rather than a super amoled screen which i've read is a little dimmer and consumes a little more power.

On a side note, I read somewhere that folks have hacked the Note so that it can use 4g on the T-Mobile network. I haven't read deeply into it.