I've no idea how good this is or how much it will cost, but I think it
is supposed to do what you want to do.

http://www.specialistantennas.co.uk/productCAE500.asp

Google for GSM repeater or GSM amplified antenna.  You'll find a number of
suppliers.  I looked, awhile back, because the apartment I moved to seems
to be in what I'll call a reception greyhole -- not completely gone, but
very poor, to the point that turning only slightly will lose signal.  The
commercial building powered versions averaged around $650 (US).  A bit
beyond what I'm willing to spend. :-)  That got me wondering if the passive
window mounted antennae intended for cars might be usable.  At $30 (again,
US), that's much more affordable.

Bill K

Hello . . .

If you get a signal outside the building, a simple wilson trucker
antenna on the roof may be the answer.

http://www.alternativewireless.com/cellular-antennas/wilson-antennas/

or on ebay at:
http://stores.ebay.com/BLACKCAT-CELL-PHONE-ANTENNA-STORE_W0QQssPageNameZstrkQ3am
efsQ3amesstQQtZkm

You can Google for "wilson cell antenna amplifier", or a combination
of those words.

Your Usenet client may wrap the above URL's if they're too long

. . . if so, copy and paste instead of clicking.

You're welcome.