I haven't used My Europe Extra yet, but have used ReturnCall on my 3 WePay SIM (getting 5p/min credit for incoming calls).
ReturnCall was discussed a bit back in January, when petkow wondered if it would be possible with a CallKey SIM, which we concluded not, for caller ID and short code sms reasons.
http://www.prepaidgsm.net/forum/showthread.php?t=1569
I suggested instead that Orange or O2 contract customers might subscribe and forward to the IoM SIM.
My Europe Extra was launched a bit a few days after that discussion, and I forgot to go back and add it to that thread as an idea
Since then, I've suggested exactly what you say a few times as a possibility with prepay O2, and I'm a little surprised it hasn't drawn more attention. In fact I mentioned ReturnCall again only yesterday, as an alternative on the thread about Voipcheap sms callback, which I'm just going to edit a bit.
Starting cost for a month in Europe would be free SIM, £10 for My Europe Extra, and £5 subscription to ReturnCall, perhaps with another optional £5 sms sent (see below)
To begin with, the RC callback was quite flakey some of the time, and now it is a bit variable in timing. The callback might take 5 seconds, 40 seconds, or just occasionally never (~5% of attempts). So you have to be patient and not try again for over a minute, or you can end up with voicemail due to 2 incoming calls; or switch off VM I suppose.
Adding a bit more complication, it is possible to use a callthrough access number as the second leg of the call, as ReturnCall forwards the caller ID, and make an onward call more cheaply.
This even works if that access number is one of the Finarea/Betamax ones, with their rates for many countries from 1 cent or penny, so on setting up an account with them, eg Voipcheap, about 40 countries can be reached for 3 pence or under, rather than the 5p RC tariff.
Another interesting number for the second leg might be the 0870 number of PlanetTalkFree, for which the RC tariff is 5p, and can be used as callthrough for plenty of other destinations, including several European mobiles on weekdays. I've only done this once or twice. PlanetTalkFree does sometimes take nearly a minute to connect, so this wouldn't be worth it for short calls.
I've kept an eye on RC for some time, expecting that the tariffs would eventually go up, but on the tariff correction of Skype to CallKey, I'm likely to subscribe my O2 to RC soon.
I wouldn't treat it as the only option though, and maybe the new sms callback of Voipcheap is a potential second string, and also usable for callthrough with RC ...
Or Voipbuster Vyke or Voxalot callback ...
If Finarea were to start similar products in other countries, then O2 Germany has a similar option for €8 a month, posted by Gryphone
http://www.prepaidgsm.net/forum/show...7&postcount=10