Like many members of this forum I rotate SIM cards at random depending on signal, network reliability, cost and my mood... Since Vodacom agreed to unlock all its data cards (and if you do indeed have an unlocked datacard) there is no reason why you should not be able to use ANY SIM in ANY data card; using the supplied datacard software (e.g. Dashboard), your machine should simply pick up most of the settings automatically and you can create a separate Profile for each different SIM card. You may have to set the access point manually by going back into your relevant Profile (in the Dashboard) and entering it manually.
For Voda it's internet, for Virgin it's vdata.
If you want to use your connection for e-mail, the incoming e-mail servers will be whatever your standard ISP provides -- that doesn't change, irrespective of which cellular network you use (unless you are using Vodacom itself as your e-mail provider through one of their free accounts, but that's another story).
Outgoing mail however needs a so-called SMTP server designation which varies between the networks and needs to be set in your e-mail client (i.e. program, e.g. Outlook Express).
The various SMTP addresses are:
mail.mtn.co.za (for outgoing use only via MTN)
mail.cmobile.co.za (for outgoing use only via Virgin)
smtp.vodacom.co.za (for outgoing use only via Voda)
(Sorry, I don't know CellC's because I gave up on them a while back after endless unresolved billing problems).
One other quick note about using a Virgin SIM: I don't know whether all the new ones are data-ready, but the older ones were not and had to be replaced on an individual basis by helpful Virgin staff. You may also have to have it data enabled through the Helpdesk.
Good luck! Trust me, at 50c/MB the effort is worth it (even though Virgin still leaves a little to be desired in the network reliability stakes -- which is why so many of us keep multiple SIMs in rotation.
