Just get TMo Web for $5.99/mo, install Opera Mini and you'll have full
access.

Yes, actually you can.

The three plans have different restrictions.

First, there's T-Zones.  It's free, and _almost_ worth the price!  It
allows WAP access to your account info, and T-Mo's
ringtones/wallpapers "store."  No "real" web access.  

Next up the food chain is "T-Mobile Web" for $5.99.  (Confusingly, "T-
Zones" was originally the name for this plan back when it was $2.99
then $4.99, so T-Mo Web is often referred to as "T-Zones" by old-
timers on places like HowardForums.)

This is the plan that non-PDA phones are supposed to have.  It allows
unlimited e-mail (POP/IMAP/SMTP) and unlimited "mobile web" access.
(What the "mobile web" is, is anyone's guess!)  You can reach any
http/https website, (whether or not your phone can actually render
them properly is another matter!) but any file downloads have to be
under 950k.  This is enforced by use of a proxy server- all internet
ports on T-Mo Web plans are closed, (including 80, the http port)
EXCEPT e-mail POP/IMAP/SMTP ports (25, 143, etc.)  All web/WAP
browsing is tdone through a T-Mo-supplied proxy server at
216.155.165.50:8080.  

Attempts to download larger files (>950k) return a "file too large"
error.  Because of the proxy, all functions except e-mail and
browsing are blocked (no FTP, no streaming audio or video, no SSH, no
VPN, no NNTP, no VoIP, etc.)

You CAN tether your PC or PDA to your phone with the T-Mo Web plan,
as long as you set the proxy server in your browser's connection
options.  (And, with e-mail ports open, POP/IMAP e-mail works fine.)  

Don't tell T-Mo, but I personally use T-Mo Web, even on my PDA phone
(recently T-Mo hasn't been allowing PDA phone owners to sign up for it,
but I've been using it for a long time, prior to buying a Windows-
Mobile PDA phone.)

Frankly, at EDGE speeds, I'm not likely to waste time downloading
anything over 1MB anyway! ;-)  I don't use mobile internet enough to
justify a more expensive plan, but it comes in handy even for
tethering my laptop when I find myself stuck in a hotel without free
WiFi.

Funny you should ask- the last plan, "Total Internet," was just
reduced in price from $29.99 to $19.99/month.  It has no filesize
limitation (it doesn't use the proxy- you connect directly to the net)
and includes unlimited access to all T-Mo WiFi hotspots.  (It's
important to note that you're allowed to use ANY WiFi device with
your Hotspot access- not just a WiFi enabled phone.  So, for
$19.99/month you'd get EDGE on your Nokia and WiFi on your laptop.)
It's the plan PDA phones like mine are supposed to use, but again, I
find the $5.99 plan more than adequate.  

Given that the Hotspots plan sells for $19.99/month by itself (with a
year comittment!) the "Total Internet" add-on is a great value, since
you can add it on, or drop it from, your T-Mo voiceplan at will.  

I didn't mention (since it's not really a "plan") that T-Mo still
allows CSD connections (Circuit Switched Data.)  It's dial-up GSM
data using your own dial-up ISP.  It's limited to 9.6k (yep, good old
9600 baud!) but there's no charge- calls count against your plan
minutes (or "free" minutes like weekends.)  While excruciatingly slow
for web browsing, it's ok for e-mail and WAP browsing (or NNTP text
group access!)  I've even used it for accessing my desktop remotely
(which is blocked on my $5.99 plan!) when I needed a large file I
forgot to bring on vacation.  Downloading it over CSD would've taken
forever, so I remote-accessed my PC and e-mailed it to myself as an
attachment, since the 950k T-Mo Web file download limit doesn't apply
to e-mail.

Let me know if you have any questions- I'm sure what I just typed was
much clearer in my head than it came out on the page!