First of all If you are not in UK/Ireland the app will tell you to that the promotion is only for UK/Ireland.
Please change your system locale to United Kingdom. How?
Win - 8
Control Panel > Region > Administrative > Change System Locale
Win 7 -
Control Panel -> Region and Language -> Location and afterwards -> Administrative -> Change system locale
Win Xp -
Control Panel > Regional Settings > Advanced
Go to - http://freeskypecredit.tech.uk.msn.com/
Step 1: Submit the name of the person who you would most like to call on Skype.
Step 2: Make MSN your homepage by clicking on the claim your credit button.
Step 3: Change your homepage back to what you previously had it set to.
Step 4: Run the downloaded file and enter your email address when prompted to.
Copy the voucher code and redeem in Skype.
How to redeem a voucher ?
Note : Last date of redeeming the voucher is - August 31st,2013.