Whilst we're talking about virtual calling cards, Rebtel is the best implementation of this I've seen. There are at least three ways to use the service:
1) The way you described: call a local number, then dial your desired phone number. It uses caller ID for authentication. Not perfect, as it can be spoofed, but likely not an issue.
2) You go online and enter the phone numbers of several people you call often. For each, the system allocates you a local phone number. So, e.g. when I call a specific local (Beijing) number, my mum's phone (in London) will ring. No PINs or double-dialing.
3) Like (2) BUT using their app and a data connection (even a slow one) you just dial the number (or choose from your address book) and their app does everything for you.
2 & 3 work because you already registered your mobile number with them. When you dial one of their local access numbers, they can combine those two pieces of information to look up where the call should go.
The call quality is great. It's a little more expensive than didlogic.com, but cheaper than Skype.
1) The way you described: call a local number, then dial your desired phone number. It uses caller ID for authentication. Not perfect, as it can be spoofed, but likely not an issue.
2) You go online and enter the phone numbers of several people you call often. For each, the system allocates you a local phone number. So, e.g. when I call a specific local (Beijing) number, my mum's phone (in London) will ring. No PINs or double-dialing.
3) Like (2) BUT using their app and a data connection (even a slow one) you just dial the number (or choose from your address book) and their app does everything for you.
2 & 3 work because you already registered your mobile number with them. When you dial one of their local access numbers, they can combine those two pieces of information to look up where the call should go.
The call quality is great. It's a little more expensive than didlogic.com, but cheaper than Skype.