mail@mail.com declared for all the world to hear...
> There used to be some sort of lookup table which told you which networl
> a UK mobile number was on. Can't find it any more.

070xx is not a mobile network, it's a "follow-me" number.

> How can I find out which network (or more importantly, how much it costs
> from a lanline or calling card) to call this number:
>
> 07096 805 XXX

There is a price list on BTs website, assuming your landline is provided
by BT of course. It's around 49p per minute.
--
Regards
Jon