Cell Phone antenna options

Okay, I’m a communications technician and reasonably savvy about radio frequencies and whatnot, and earlier tonight, a guy walked into my office asking for advice on a problem. He wants to use his cellphone at an isolated cabin about 30 minutes from the nearest town. So far, conventional portable antennae have proven useless, so he’d like to install a permanent antenna on top of a nearby hill, with cable running down to his cabin. A fast search of the net finds manufacturers of antennae to be mounted on boats and whatnot, the largest I’ve found is about eight feet.

Now, I could rig up an even larger dipole directional antenna with BNC cables and amplifiers and whatnot, pointed at the nearest town, but before I do that, I’ll ask among the Dopers if anyone else has tried installing large antennae for cell phones and what problems they may have encountered.