I would like to get rid of my land phone line. The only thing keeping me
from doing this is the relatively poor indoor reception on my cell phone
(outdoors is just fine). I can't justify spending $700 for a powered
repeater set-up, but since I get good outdoor reception, would it be
possible to couple a dual frequency (800 & 1900 MHz) high gain (36 dbi)
directional antenna directly to an indoor multi directional unit (both 50
Ohm impedance)? This would only cost a couple hundred bucks, but will it
work in theory? Any advice or
other suggestions would be greatly appreciated.

While passive repeaters are often used, what kind of antennas are you going
to use to get 36 dbi ?