If you are using the Telecom supplied MF626 (I havent tried any other ZTE devices) then you are going to have issues running it under 64bit Snow Leopard using the Telecom Connection Manager.
Here's how I got it going;
1. Plug in the mobile data stick.
2. open the 'Telecom Modem' icon located on the Desktop or in Finder.
3. Right click 'Telecom Connection Manager' and click 'Show Package Contents'.

4. Navigate: Contents > Packages - then install 'app'

5. I downloaded the Vodafone Connection Manager from http://business.vodafone.com
6. unzipped and mounted the disk image.
7. Right click and select 'Show Package Contents'.

8. Navigate: Contents > Resources
9. install whichever drivers you need, in this case for the MF626' ZTE Data Card Driver Installer.pkg'.

10. close all windows and dismount all volumes which were mounted during this (Including the 'Telecom Modem' volume.)

11. Remove the USB Modem.
12. Open the 'Telecom Connection Manager' and plug back in the modem.
From what I can tell, the 'Telecom Modem' volume will continue to mount each time you plug it in - however, it's just a matter of ejecting it, then it will initialize the modem.
Now everything should be all go. If not, restart your Mac and try opening the Connection Manager again and plugging the USB in.
PS: don't try and use the Vodafone connection manager - I couldn't get it to work/work properly.
NOTE: For those who dont feel like going through that:
ZTE Driver
Telecom Connection Manager App
PS: Apologies for the numerous edits etc - been trying to rush this out so I can get to bed! :P