[FOSS-GPS] DGPS for newbies?

[Timo Jyrinki]

What would be the best resource for information about DGPS? I gather
that DGPS is the term that is usually used about GSM base station id
collections, to help getting approximate coordinates, or are there
other meanings? What resources are free (as in freedom), or is the
scene currently dominated by restricted providers (like jaiku?)?

What various aspects the information is used for - is it only used to
get approximate coordinates so that AGPS information (satellite
formation) can be fetched by using the approximate coordinates to
fully automate the way to get current satellite data, wherever you
are?

With the whole plethora of terms, and the fact that "Assisted GPS" is
used to mean quite many things, it's sometimes quite easy to get lost.
I guess what I would want is to have a DGPS database I can use to get
approximate coordinates so that I can use the AGPS tool on my Neo
FreeRunner to fetch current satellite data from u-blox... for now.
Currently I'm just assuming I'm not more than 250km away from home,
but if I'd be elsewhere I should manually change my agps parameters.

-Timo