Henry VIII wrote:

> In my case, however, I have to determine my geographic
> location independently of GPS. All I need to do is to relate
> a GSM tower's cell ID to a location very roughly. But even
> that rough tower location data seems to be unavailable.

I was thinking that you might be able to map the locations for
yourself as a separate exercise, prior to your implementing
your proposed main system. This would involve writing an
additional purpose-built application to initially correlate
GPS, cell ID and TA data as a foundation for the real
application.

How feasible this is would depend on the geographical area you
want to cover. Obviously, covering a significant part of a
country the size of the US in this way would be completely out
of the question (except for a large organization like google).

> I assume a way around this would be to purchase an API from
> every service provider, but this involves considerable
> expense, and there is no assurance that all providers would be
> willing to do this.
>
> So ONLY the network service providers can sell tower-based
> geo-location services (ie - triangulation) because they alone
> have the tower location data?

I agree that the secrecy is likely motivated by purely
commercial concerns.

John