Thanks Ash, Yes 20 hour's ( 1,200 Mins ) per month is the maximum of allowed free calls, I've just worked out what the wife has used and her free calls come to a total of 800 Mins with 400 of free calls available till 29th May, That works out at 20 Mins a day of free calls.

20 hour's a month works out at 40 Min's a day of free calls which is still a great deal, probably still the best around without a doubt, As long as you keep tabs on your free time usage there should be no problems.