If you travel a lot Skype has a fantastic service in SkypeIn. This allows you to have a "telephone" number that belongs to your Skype account. The numbers that Skype allocates are geographic (unlike some other VoIP services who offer non-geographic, and therefore more expensive, numbers). There is currently a choice of numbers based in 20 countries.
Let's imagine you live in the UK and travel frequently to the USA. Get two SkypeIn numbers. A USA based number and a UK based number. Your USA contacts can call your USA based SkypeIn number, wherever you are in the world and pay for a USA local call. Your UK contacts can call your UK SkypeIn number and pay for a UK local call, again regardless of where you are in the world. How cool is that? A huge money saver for contacts who call you from a landline or mobile phone.