If you play it smart, you can use this promotion to get free calls forever (until they cancel the promotion at least).
Here's what you should do:
1) Make a Skype account (or use your current one) and grab your free month here. You will need to enter your payment details but don't worry; they won't charge you anything until the beginning of the next month.
2) Cancel your subscription as soon as possible. If you forget to cancel it, they will automatically charge you for your next (paid) month of subscription after 27 days.
3) Make a new Skype account, name it something like username1 so it's easy to remember. Currently they don't seem to have a rule to prevent new accounts from using this promotion, but I think it's safer to make the new account on beforehand.
4) Make calls, enjoy life. Make sure to put a note in your calendar so you don't forget when your free month is over.
5) When your free month is over, get the promotion with your new Skype account. Repeat this process as many times as you want.
If you're using your Skype account for anything other than calling phone numbers, this approach might not look very attractive to you because you will have to use a different Skype account for calling phone numbers. Fear not, there is a solution to this. You can run two instances of Skype on your computer. For this, you should make two shortcuts on your desktop.
I'm sure that you know how to make a shortcut for Skype on your desktop. For the second instance of Skype, just make a second shortcut and enter /secondary at the end of the target address. It will look like this:
32 bit:Now you can have two instances of Skype running: use one for calling phone numbers and one for your normal Skype stuff. This approach is working perfectly for me so far. Let me know if you experience any problems with this.
"C:\Program Files\Skype\Phone\Skype.exe" /secondary
"C:\Program Files (x86)\Skype\Phone\Skype.exe" /secondary
*Countries with free landline calls: Andorra, Argentina, Australia, Austria, Belgium, Brazil, Brunei, Bulgaria, Chile, Colombia, Costa Rica, Croatia, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Guadeloupe, Hungary, Iceland, Indonesia (Jakarta), Ireland, Republic of Ireland, Israel, Italy, Japan, Korea, Latvia, Lithuania, Luxembourg, Malaysia, Malta, Mexico, Morocco, Netherlands, New Zealand, Norway, Panama, Paraguay, Peru, Poland, Portugal, Romania, Russia, Slovakia, Slovenia, South Africa, Spain, Sweden, Switzerland, Taiwan, Turkey, United Kingdom, Venezuela.
**Countries with free mobile calls: Canada, China, Guam, Hong Kong SAR, Puerto Rico, Singapore, Thailand, United States.