Would you like free, unlimited calls to: Australia, Austria, Belgium, Canada, China, Czech Republic, Denmark, Finland, France, Germany, Hungary, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Taiwan, United Kingdom and United States?
Here's how to do it:
First download a Skype-like application to yur PC from here, install it and use it to log in and create a user account (no cost). Following that you can make free calls via your PC up to 1 minute to any of the above countries. If you then add credit to your account (credit card required) here (minimum is only 1 Euro + 7% Swiss VAT) you can make unlimited free calls to the same countries, plus cheap calls to many others (complete list here). You don't even need to your their softphone application- using the SIP registry www.voipbuster.com and the same username and password that you registered with you can also register any SIPphone/ATA so can use a "real" VoIP phone if you have one.
You also get a number for incoming calls (mine is in Hannover), but I've had no success in using this. Don't really care about this, however, as the the advantage is mainly for outgoing calls.
I can't say if there are any catches, but neither can I see any. I signed up yesterday and added €1 credit to my account. I've confirmed with my credit card company that only €1 was deducted. I've also made more than an hour of calls to USA, UK and Australia, and my whole €1 credit remains intact, and there have been no further deductions. I suspect this may not be a long-term offer however... I have some reasons to believe that this (apparantly Swiss) company may be related to the UK call-by-call provider Call1899