I can add a bit more.
If you have access to a land line ie:- hotel then there is a cheaper way.
Sky, Virgin, Orange, and talk talk home phones have international calling phone addons for £2 a month.
I have this, so the following works for me.
Text the Mrs the hotel room direct dial No when i check in, normally on the phone or in the room info booklet.
She knows when i am on business not to answer the mobile straight away and if i ring and stop then she calls the hotel on the land line.
If the hotel doen't do this, then i use the same process but reception puts her through.
Failing that on very rare occaisions I am with Voda and have a family pack, with this I pay a 75p connection charge and the calls are free. (but only when she rings me when abroad).
Have been using this method for the last 10 years whilst travelling to Germany, Spain Italy and Ireland no problems.