HOP can be pruchased from distributors like www.telestial.com or direct from www.hopmobile.com

I use itand I am pleased. The only place I ever had a problem was Kuala Lumpur.

I suggest visiting the HOP site above and get information or the Telestial site which has tons of information/options etc.

When I found the actual hopmobile site (Europe), I registered my credit card with them and I can now refill my sim on line from any computer in the world. Just logon, with password, enter a code they give you and tell them how much value you want to add. If you buy the additional time from Telestial they will charge you a premium (like $65 for $50 worth of airtime). www.hopmobile charges no premuim, $50 gets you $50 in airtime (.35 incoming and .99 outgoing).
I'm taking the phone to Beijing next week.