I can't get Network Positioning to return a location when using my T-Mobile (USA) SIM.

When using a borrowed AT&T SIM, a position is found in a handful of seconds.

With T-Mobile, enabling Network Positioning in the Location settings then selecting Street/District/City-level within My Availability > My Location shows a flashing satellite dish icon... forever. The status shown under Location when tapping the clock is always "Searching".

Workaround found: Use supl.google.com instead of supl.nokia.com and reboot. Follow the link for more details.

Some diagnostic steps I've tried:

It's not that the cell ID is unavailable from T-Mobile. Using dbus, I can successfully get information about the current cell:
A T-Mobile technician confirmed that the 278XXXXX number matches their cell ID scheme.

It's not that the outgoing port (7275) is blocked by T-Mobile or that the supl.nokia.com server is unresponsive. I can apparently connect to supl.nokia.com via wifi or T-Mobile 3G from the N900 with socat:
To further test this, I set up a TCP relay on my home machine, forwarding connections on port 7275 to supl.nokia.com's port 7275 and pointed the Location Server in the N900's Location settings at my machine. Capturing traffic on port 7275 on my relay machine and using socat on the N900 like this:
I observed a successful TCP connection made from the N900 to the relay, both over T-Mobile 3G and wifi.

Disabling and re-enabling Network Positioning does not appear to trigger a connection attempt from the Location service. However, with this relay and capture setup, on booting the N900, I observe what appears to be a successful connection to the relay, some binary data is transmitted from the N900 to the relay and sent along to supl.nokia.com, the response that comes back looks all SSL-ified, and that data is sent back to the N900. I can understand this probably not working properly due to the TCP relay of SSL data -- that's not the point. The point is that the N900 is trying to connect to its configured Location server, and it is sending some data and getting a response.

So, with the Location Server set back to supl.nokia.com, the connection is presumably made, but either something about the response isn't acceptable to the Location service, or something later in the process is hanging.

The location service never seems to retry the TCP connection. Perhaps the response is cached and re-used or perhaps the service is basically hung. The satellite dish icon just keeps blinking.

dmesg shows nothing of interest.

dbus-monitor --system, when run while enabling and disabling Offline Mode, shows that a dbus call of some sort is being made that returns the cell ID.

Is there anything further I should look into to determine why a coarse position is never obtained via T-Mobile? Or hopefully even fix this?

what if you use different location servers??

I had similar results (though not nearly as articulate )
Someone suggested contacting Nokia technian with the details of the error.

Re: Using other servers

Please suggest some. The T-Mobile technicians I spoke to did not recommend any alternatives. iIn searching, I found mention of several *.3gppnetworks.org servers, but none I tried would even resolve via DNS.

I've spoken with T-Mobile twice now. Unfortunately, there is no "error" to report that I've found, and a similar service on other devices (Google Maps on the G1) works fine.

Yes, I am also seeing the same problem on T-Mobile here in New York. never able to get a location fix.

Which technicians should we be speaking to?
t-mobile? - Its not a network error.
Nokia? - Its not a hardware issue.

I'm on T-mobile. I get a lock. If I turn off Network location I never get a lock.

Is there a way to enable debug logging on the Location service?

I don't have a good answer, but I do get nearly instant locks with my T-Mobile SIM (USA/Bay area CA) - I did have an AT&T SIM in the n900 for a little while and it seemed to take a bit longer to lock, but it got there too.

Under Settings/Locaton

GPS Enable checked
GPS Device Internal GPS

Network Positioning
Enable Checked
Location Server: supl.nokia.com

Do you have a data connection up?