Go-Sim
 

Has anyone used it?

http://www.gosim.com/

If yes, what are your experiences with it?

I haven't used it yet but I think it can give me sort of convenience and cost savings while in travel. I have a friend who tried it because she always travels due to her job so she uses it and find it really cool!

Yes, I've used Go SIM, they're very good. I had a few issues with them a few years ago while travelling the US, but they seem to have changed providers for their US SIM card and it's both cheaper and better quality than it used to be. Also, their data rates are pretty good at the moment. They've also got an excellent customer services team who can troubleshoot most issues for you, so consider this a recommendation.