I am based in UK, but I frequently have to travel around the world
with my job.  I have a company mobile phone based in the UK, and I can
use it anywhere in the world, but I often incur very high bills for
the company because the roaming charges can be very high.

Sometimes, I will buy a pre-paid SIM card in a local country and take
a new number temporarily during a trip, which can prove more
cost-effective even if it's a bit inconvenient to change my number for
a limited period.

This leaves me with a problem - I know very well, of course, the
various tariffs of the mobile phone companies in the UK, but I have
little / no knowledge of the  mobile phone companies and tariffs in
the countries that I visit.  What I therefore need to find somehow, in
a single website, is someone who is collating information on local
tariffs offered in countries around the world.

I would expect the solution to this question to include most or all of
the following points:
- likely to be a site which is orientated to business travellers or
other travellers
- shows clearly the rates of calls (incoming & outgoing) of the
tariffs, both to local destinations and internationally (most of my
calls are back to the UK)
- includes both pre-pay and contract-based options (sometimes a short
contract would be more economical)
- considers the option that it may be cheaper to buy a pre-pay mobile
phone (including handset), take the SIM card out and use it in your
own phone (because the rates can be lower than on a SIM card aimed at
tourists)
- includes what features are available on the network (frequency of
signal, GPRS or UMTS available, etc)
- for pre-pay, the method of top-up available (by voucher, by ATM, by
credit card on phone, by internet)