I make quite a few international calls and in the past I had played with Skype and had quite a few problems setting it up alongside NAT and the local firewall. Well today I found a voucher for some free airtime using SkypeOut in amongst a headset I have bought so I thought I would give it a try.
I installed the latest Skype beta for XP (Linux/Mac clients are also available) and it just works fine. SkypeOut lets you call people who only have landlines available and the quality certainly seems acceptable. Skype-Skype calls are free and the land line rates are a little high for local calls (UK), but hands down beat our existing supplier (Telediscount) for calls into Europe.
I need to do some more work to see how it behaves in an office situation, but I'm already seriously looking at some of the toys^H^H^Htools they offer.