Paul, it sounds to me like you've already sorted it out. Here is how I would outline the choices:
1. With Skype, worldwide voice comms are possible computer to computer. Many of us out cruising use this regularly if a) we have broadband (e.g. wifi) connectivity, or
we're wintering somewhere, even if we only have a phone and so slow modem. We've used this in London at terribly slow baud rates but, with some disconnects, it made many things possible that would have been expensive, indeed.
2. With SkypeOut, you can access N American & European conventional phones. A friend who's wintering in Cascais, Portugal just had his wallet picked, and due to Skype was able to deal easily with all the USA credit card issues (don't carry a wallet full of cards!) This also makes using toll free #s possible, which can be inaccessible when outside the home country.
3. VoIP disguised as 'regular' phone service, where a phone number for a given location is purchased; broadband required plus a 'modem' of some kind. Vonage has a million customers now in the USA and is of this type. SkypeIn is another alternative, tho' I don't know if a modem is needed. I'm told E Asian programmers on H3B visas who work here in the U.S. send Vonage modems back home (where broadband is abundant), and their family can now make "local" calls to all the relatives thru-out the USA. Same as your story about a 'London phone number'.