A friend of mine is getting one, as she doesn't want to get roaming charges during her vacation, but still wants to talk to people on WhatsApp. Seems to solve this problem quite well. :)
Assuming you're in the US, has your friend considered T-Mobile's Simple Choice plans? Text and (throttled) data roaming is free in dozens of countries, and voice is only 20c/min. Skype and FaceTime Audio is perfectly fine on the throttled data, too.
She could get a 3 SIM if she's from the UK? "Feel at home" countries have the same freedom as being in the UK, so the £15 PAYG SIM (which you can stop using after a month) gives you 25GB data, unlimited texts and a large number of calls, even if you're in various countries in Europe, and even better, America. I will be looking to use one when I visit America later in the year.
I've used Feel At Home quite extensively (more when it was still called 3 At Home) and it's fantastic. The two countries I visit most often, USA and Spain, have recently been added to the list. I'll be able to get rid of my international SIMs and cut out the logistics of having to swap then while travelling. Free data roaming is just about the best thing a network can offer customers who travel.
Glad to hear it works well, as I am currently with TMobile and was horrified by the prices for going to the USA. I may even switch to 3 for my "daily driver" phone.