I'll go with some of the earlier suggestions, and comment on my personal experience
* Skype - Skype is great especially if you have a decent internet connection, and with Fast ADSL available at reasonable prices its the way to go. For those who don't know, Skype to Skype calls are free, and Calls to Landlines and Mobiles worldwide are very competitive. You can just pay as you go, or get a subscription for Unlimited calls to one country (€4) or to 40 Countries (€10) which is very handy. You can also get an incoming number for dozens of countries so non tech savy friends and family can call you without have to know a computer from a cantaloupe
There is also a Skype Phone available, either direct from Skype or from other resellers which allows you to be connected to Skype without having to have a computer running. Its called the RTX Dualphone 3088 and consist of a base station which you plug into your Internet router and a cordless handset which you can have anywhere in your house. We actually have two of them running in our house as we have one personal and one company skype connection running through each and it works great.
* Vonage - If you don't want to have to think about setting up a skype account or using a computer or even setting up a dualphone, consider getting VOIP service from a provider like Vonage. Setup is Dead easy. Plug in one cable into your router, and then plug in any phone with a standard (RJ11) jack and you are up and running.
They have plans starting from £6 (In the UK, More later) to £18.99 and you can chose which one will work for you depending on which countries you call regularly. All Plans include one incoming number, Voicemail, call forwarding, Caller ID, and Itemized Billing (Good for getting reimbursement) . You can also get incoming numbers from countries other then your home country for £3 a month so if you have Business or relatives there you can give then a local access number for a low cost.
Now the big DRAWBACK. Vonage requires a billing address in the country where you buy the device, so if you buy one in the UK, you need a UK card and billing address. The service is available in the US, Canada & UK(Though the UK site does serve Spain).
* Vodafone - Vodafone has just introduced a new international calling service, which has reduced the previously astronomical international rates to merely high. if i remember it correctly you can either chose to pay a fixed fee (6 or 7 L.E. pm) and get international calls at L.E. 1.99 (Down from L.E. 4-5) or chose the Pay as you go version that they charge you a setup fee. This is handy if you often need to make calls when you are out and about.
We use a combination of all three as we have to make a lot of international calls, and it has made a drastic difference to our phone bill.
Hope it helps.
