I use Skype, and I do not pay a monthly tariff. Instead, I pay as I need to, topping up the account by credit card. Skype itself is free to use from computer to computer (as long as both computers have a Skype account) and I pay when I wish to contact/connect with a land line (which is extremely reasonably priced), and pay a bit more when I wish to contact/connect with a mobile phone.
Cheers