I've used the SkypePhone 1 and 2 but passed on grabbing an INQ1 simply because I don't need more and more devices but with all the hysteria about Skype on the iPhone I am likely one of the few in the USA who have used the original technology that Skype is referring to in their accounts about driving additional revenue to carriers.
The technology which 3 is using though is not from Skype. It is from iSkoot which installs a box into the network that takes real-time Skype presence data, then works with the mobile operator to bridge the call over the cellular carrier's circuit switched network.
The service, which for someone like me who visits the UK about once every 6-8 weeks (or has been it seems) is very attractive. Buy a Skype/iSkoot app capable phone that works on the Three network. Obtain a pay as you go SIM and top it up. The top up never expires but to use Skype you need to purchase a top up at least once every 90 days (it used to be 30 days) and when one gets to a country where Three operates, simply turn on data, by purchasing an add-on for Internet for a day, a week or a month at a rate of .50 pence, 2.50 pounds (for the week) or 5 pounds for the month. What I like about the Skypephone2 is you can also use it as a 3G data modem (tethered) to a PC or Mac.
The call quality on 3 has been stellar when I've used it. Last week I loaned one of our two units to my wife one to use to check in with her office last week, as her staff is reachable on Skype and her ability to be reached was simplified and the cost other than the 2.50 pounds for the week was nothing compared to what calls would have cost her on her AT&T phone when roaming internationally. (Note she also made extensive use of her Truphone via WiFi and Truphone Anywhere on a spare N95 we carried when in France too.)
Sadly, while many of the carriers were offered the iSkoot solution, only 3 has taken it up. Now 3 was built to be an all 3G network, but has never achieved the consumer or business uptake in the UK the way Vodafone and Orange have. My experience has been nothing less than stellar with the devices and the call quality. What's more the recent addition of pay as you go data with inexpensive data cards has been a big benefit for me.