I believe it is appropriate to sound some caution about this service, not least because of the chaotic state of their website!
Although the first page shows several discounted rates, these are NOT shown when you navigate to the appropriate country calling rates' pages.
For example, your India rate of 3p is shown on the first page, but India landlines are shown as 5p, and India mobiles as 7p, on the actual country rates' pages.
Similarly, Pakistan is shown as 4p on the first page, yet 7p and 7p on its country rates' page!
In view of these lamentable discrepancies, I would suggest that nobody knows the true calling rates without making some test calls, and I for one am not going to buy one of their SIM's to find out!