You should almost always buy your IDD separately from your basic service subscription. Do you have a particular need for phone cards? IDD services from people like IDT1529 or HGC 0080 or PCCW 0060 are easy to sign up for and you just pay for what you use. Personally I have accounts with all three, but use IDT1529 as my primary IDD supplier at the moment - the quality is very solid, and they do less rounding up than PCCW (which rounds calls to the next 10 cents as well as to the whole minute).
Calls to UK mobiles cost about HK$1.80-$2 for good quality. India is a very dynamic market at the moment - some operators are trying to drive the price down, but quality is suffering with some as well. There is a wide range of offers from HK$0.30 up to HK$1.50 - we need a recommendation from someone who calls there a lot. But even then, the quality can be quite dependant on which operator the Inidan customer is using - some IDD carriers have much better connectivity to some Indian operators than others.