Just be careful .... I recently had a MTN claim rejected initially due to me using a different MTN sim in the phone other than the original MTN sim I bought it with. It was only after I asked them for proof of them sending me the terms and conditions of the contract that they realized they never sent it to me and they honored the claim.
Bottom line: I'm not sure this 'scare tactic' will sit well with the CPA but I suggest you rather play it safe than sorry. And for what it's worth .. If you're going to buy cash, you may ask well rather look at contract from Cell C. It works out only slightly more expensive (if you multiple the monthly amount by 24 for the 16GB phone) than the actual cash price of the phone and you get so much more value ...