+44 ?

International dialing - country calling code for the UK...

International code - country code - (area code) - subscriber's number

From Wikipedia...

The telephone numbering plan for a telephone system includes an international dialing prefix, such as "00" or "011", which is added before the country calling code and is specific to the country from which the caller is dialling. Generally, as in the list below, the need for this prefix is indicated with a "+".

Peccavi
March 2010

It means it has come from UK number, 44 is the international dialing code for the UK

nigel
March 2010