There seems little point trying to expend a lot of time and effort in order to duplicate the resources readily available elsewhere.
Why should we want to 'reinvent the wheel' ?
Both niftylist and Joel's group already provide handy tools for looking up the cheapest call providers for calling different countries and call types.
Joel's website at
http://www.ourfavouritecompanies.com/ gives links for looking up all sort of call types - see the middle of his page.
The niftylist call checker is found at
http://niftylist.co.uk/calls/and gives options for looking up calls to landlines and those to mobiles.
Both sites occasionally feature better rates than the other, so it does pay to look at both I find.
A case in point is that, at the time of writing, Joel's group gives call rates of both 2p and 2.5p for calling Pakistan, for example, whereas the cheapest showing on niftylist starts at 3p.
( Compare
http://www.ourfavouritecompanies.com/Peak/phone-rates/Pakistan.shtml and
http://niftylist.co.uk/calls/to/pakistan/landline/ )
mobaholic.