If that were true, why would anyone ever spring for one of the more expensive 'Smartphone' data plans? Why would they even be offered?

The $19.95 plans are only for 'feature +' phones, ones that T-Mo knows aren't capable of the kind of data usage true smartphones are. And only locked ones, I'd wager.

Trust me, the smartphone plans apply to the N900.

I'm on T-Mobile in Sacramento California and here is a statement of my services and fees associated with it (maybe it can help shed some light on the subject):

Monthly charges $69.98
Block S/MMS SUB $0.00
Get More 3000 $49.99
Total Internet Addon $19.99
Use charges $6.88
LOCAL AIRTIME, LONG DISTANCE and INTERNATIONAL CHARGES $6.88
One-time charges $0.00
Credits & adj. $0.00

Other charges $1.21
Regulatory Programs Fee* $1.21
Taxes and Fees $6.96
CA Advanced Services Fund $0.13
CA Relay Service and Communications Device Fund $0.11
California High Cost Fund - A (CHCF-A) $0.06
California High Cost Fund - B (CHCF-B) $0.13
California Teleconnect Fund $0.04
City Utility Users Tax $4.15
Emergency Telephone Users Surcharge Tax (911) $0.29
Universal Lifeline Telephone Service Surcharge $0.62
Total New Charges $85.03
Previous Balance $79.17
Whenever Minutes 3000
Data Usage Unlimited

Geesh, I couldn't get the formatting to fit correctly. My normal monthly bill is $79.17 after taxes for 3000 minutes and unlimited data.

The phone I use is the Sony TM506 but T-Mobile only knew that after I told them. Until then, they thought I had a five year old phone with this plan.

The smartphone plans aren't so much "offered" as "forced down your throat" when you buy a subsidized smart phone from them on contract. AFAIK, they are the same "internet"...just different prices due to the increased usage that the typical smartphone user incurs.

To end all this, the regular internet package is edge access only, while the smartphone plans have fast edge or 3G. Some non smartphones can also access 3G, but qualify for the regular internet because of their low data usage, and are usually branded phones.

The real secret is that if you have an unlocked phone, just walk in, pay a plan's first month bill, and go home. Once you're on for 24 months, you can get a loyalty plan that gives you unlimited voice for $55 a month for one line, $95 for two, and adding data for both is just $70, making it $125 for one or $165 for two lines with unlimited messages and data.

They don't heavily enforce data caps unless the network is congested, and it never is, but its 5GB I think. TMobile is very open and lenient on data. I've used their data cards for torrenting and P2P, and it never caused an issue.

There's a difference in the plans. One gives only Edge access except for select feature phones, and the other is
3G with full open ports.

I was doing a little research on the pay-as-you-go plans,and I saw something that caught my eye. It appears you can pay by the day for $1 per day, for each day that you use t-mobile's service. Down towards the bottom of the webpage (see link below) it talks about sidekick users getting unlimited IM, texting, messaging, and web browsing for $1 per day, and talk time is $.15 on top of that. That means pre-tax, you could theoretically use the N900 everyday always on for around $30 depending on the month, if t-mobile put the phone on the sidekick plan. Under the prepaid phones, you can also buy just a GSM sim card to activate and slip in the N900 for $6.99 w/online discount. Does this whole scenario sound reasonable, or am I missing something? Would this really work for the N900 to be a "data only" internet tablet for around $30/month sans voice?

Here is the website talking about the pay as you go plans.

http://www.t-mobile.com/shop/plans/prepaid-plans.aspx

Do some Google searches on this plan. Until recently, some iPhone owners were doing exactly as you propose. Due to that though, T-Mobile recently began "fixing" the the PAYG Sidekick plan.

T-Mobile has at least blocked port 80, and I've read conflicting forum posts regarding what else they may have done--and what they may be doing in the future. Actual Sidekick users have been unaffected by the changes, but most of the iPhone folks appear to be fleeing back to AT&T.

In a few forum posts, there's been talk of slipping past T-Mobile's blockades via proxy servers or VPN connections, but most of the writing appears to be speculative.

There may well be a suitable workaround, but please be aware going in that the PAYG Sidekick plan may not be an "drop the SIM in and go" solution.

I broke down and called t-mobile. I explained the situation, and they said to do data only on a "device" like what I described, the T-Mobile Total Internet plan was the way to go. No annual contracts, just straight up internet unlimited, and voice calls if you wanted. 39.99 per month, so around $50 with fees and taxes depending on state. That's higher than I want to pay per month just for the novelty, plus I get way better coverage with Verizon and tethering my EVDO rev.A BB up to it. I just hope they get the BlueZ team gets the DUN protocol up and running for the N900 for us weird tether a phone to a phone kind of folks. What can I say, Verizon's service and more importantly coverage are too vast to compete with. Food for thought anyways.

Monthly charges - $99.96
Faves Unlmtd Loyalty $49.99
HotSpot Unlim-Monthly $9.99
Intl Disc Call Mobile $5.00
Msg Value Bundle UNL $14.99
VPN Total Int Addon $19.99
WorldClass Int'l Rate $0.00

I spend on average 4000 minutes of talk and 100-300M data a month w/ my 5800. I expect data to increase with an n900

I've been tethering my n810 over the $25 Unlimited plan for a few months. No complaints.

Speed tests show about 20-25Kbytes down, 12kbytes or so up.

I'm told the difference between the 25 plan and the 9.99 is that the 25 has zero port restrictions, ie IM voice p2p https ssh etc work. The other is run through a bandwidth/port restriction limiting proxy.

I'm currently using google voice to make all my calls with my GV number set as a MyFaves (meaning unlimited minutes)...so for the cost of a data plan (I share a family plan with others) I get unlimited minutes, texts, and data!