erm well, I have a month to month contract with them so i don't think it would be any haslle? unless you have a two year contract then it could get messy..
I did it with a smile on my dial I had more problems with Vodacom 3G then you can imagine!! All i did three months into the contract, I packed eveything up walked into the Vodashop where i got it, and gave everything back to the lady who did the contract for me. Then told her it "i don't want it because it doesn't work and i want her to cancel it" then walk out and went to the bank and put a stop on the debit order and never heard from Vodacom since! they didn't even try to take the debit order the following month. Well why i did this is because i only connected like 10 times in the 3 months of having it. And i complained and complained with no luck, Vodacom kept telling me it was my pc but now i am on virgin and no problems
Costs would be the remainder of your contract and your SP might add in a penalty charge for early termination, you would have to check your contract for that... and you may have to hand your card back or you can pay for it.