Indoor mobile reception

We've got one of these mobile phones with an hour's free off peak calls
a
day, so we tend to use if for most outgoing calls. Reception outside
is
excellent, but inside although usually OK, it sometimes goes
borderline, and
I reason that there must be a relatively simple way of resolving this
(thinking for example about the pig tail car aerials). We've got wood
framed DG, so I can't put anything across a single pane of glass, but
making
holes through the frames wouldn't be an issue.


Am I kidding myself that there is a simple solution? Has anyone else
tried
to sort this problem out?

Denis