Biggest problems seem to be the existence of different-length numbers, and not knowing which prefix codes to use.

e.g. I have a friend's number, which is 1538180*** (last three numbers have been blocked out). Can anybody tell, simply from looking, if this is a cell or a home number? If so, how?

Argentina is +54. So I would assume that my dial from Skype should be +54153810***. But, it doesn't seem to work.

Anybody got any tips?