Hi there Paul,
You're right about playing on either CN1 or CN5, although CN1 is probably more densely populated.
There is, apparently, a large group of English speakers that do PvP (I think) on CN1, well-integrated into the Chinese community on that server. I believe that they're on
山丘之王/Bronzebeard, Horde-side, with their guild name being 朝九晚五.
Also, there's an Alliance guild on 玛多兰/Madoran with a significant number of English speakers as well (I think). Their name is the Cow Eaters.
Feel free to look both of them up.
I don't believe that you'll be able to use an international ID, although feel free to try ---- you can always call their Tech Support and see if they have anyone that speaks English
If I were you, I'd start looking for a pal who'd be willing to lend you his ID card. Hah!
I don't have any experience with CNMobile, but Unicom's CDMA is rather reliable, in my experience. Either way, I'd suggest getting some kind of land-line, they're FAR more reliable!