get one with a +44 number and calling iceland, estonia, lichtenstein is difficult from many countires or pricing seems to be very high compared to a +44 based card.

Having a did number is nice but you are paying for the forwarding cost and these are not low compared to just making a call to a +44 number.

If you choose one, look at a reliable one. Meaning many companies have rates on there site and you get charged differently. Or you get charged when the callback is activated even if the called party does not answer (maxroam for example)
I have been using united mobile for a while. Maybe not the cheapest but they have a reliable background for some years now and do not switch from one platfrom to the other like many other companies.

Even UM is problematic. Last September, after converting to UM+, callback did not work for me in Austria. I don't mean that it sometimes didn't work but rather that it didn't work. Period. For the entire three weeks that I was there.

Now that may have been related to teething pains with the switch to the UM+ platform but nevertheless, if I didn't also have a Mobal SIM I would have been stuck.

But I agree, most of the time UM+ seems to be a good option.

I've used UM+ in Austria and had no problems...

One of the problems is that for some reason it seems some carriers try to block access to UM or UM+....the solution is to manually select a roaming carrier...I've had cases say in France where I couldn't get it to work with Orange FR but it worked flawlessly with SFR.

Just out of curiosity, did you try to manually set the roaming partner?

Interesting. That wasn't an issue for me with UM "classic" but it certainly makes sense. However, that's not a good "feature" for someone like the OP who wants to deploy across a company with many users, not all of whom are cellphone "literate."

No, but since I'm leaving for Austria tomorrow I'll soon have a chance to try it ;) Thanks for the hint.

www.goglobalsim.com offer a good referral programme also