Disclaimer: I am giving my own account of these services, and have not been asked for nor compensated for my comments.
Overseas calls, especially from mobile phones, are hugely expensive in Europe. Tariffs are generally in the 1 GBP (1.2 Euro) per minute range, and may include additional fees for network access. I recently discovered that calls between the UK and the Netherlands were being billed at the same rate as calls to Chicago, which was a shock. EU lawmakers and regulators have been trying for years to reduce roaming charges, but they are still very high by American standards and unlikely to change in the near future.
As a result, I rely heavily on Skype for international call services. It works very well when both parties are members of the service, and I get good voice quality even on slower DSL connections. The text, video, and call conferencing services are also very useful; my only complaints are that file transfer rates are abysmally slow 
and Facebook integration is a needless complication. New ‘version 5.0’ features include the ability to log onto local internet services using Skype billing while on the road: not as good as ‘free Starbucks or McDonalds access (Amanda has a good review), but useful in a pinch at an airport or train station.
I added call forwarding (Skype calls forward to my cell phone), Skype Out (call from Skype to land line and mobile numbers), and Skype-to-Go (dial into Skype to call internationally at reduced rates) in support of my business. However, since I registered with Skype from the US, Skype uses US rates. So, while domestic calls are cheap, international ones are expensive. This was driven home when I discovered that local call forwarding of Dutch numbers was being charged at international rates (below). Beware!
I’ve recently registered with another reduced-rate provider, OperatorOne. Unlike services that bill through the mobile phone account, these folks set up dedicated local dial-in numbers for each overseas number that I call. My mobile bills only for the local call, and long-distance charges deduct from credits that I leave with OperatorOne. So, here’s an example of my billing:
It works pretty seamlessly: the only glitch that I’ve found is that the local number doesn’t hang up automatically if the long-distance caller hangs up. Thus, I had a one hour ‘local call’ consisting of dead air when I didn’t notice that the phone was still connected even though the call ended.
