That would be silly, because then he would have no blackberry service.
The way MTN bills is that you have your Anytime 350 (as an example) at R350 per month, then the promo fee of R99 (as an example), then blackberry BIS of R60 and then a blackberry service discount for R60 as the contract loaded is an Anytime 350 @ R449 per month including BIS.
If he cancels the BIS service on the 1st as you suggest, then he would be paying R449 per month and get no blackberry service and no discount.
How do I know? I've tried it....
On my GF's contract, she had BIS loaded already, and when the upgrade including BIS kicked in, MTN just added the discount to make the BIS effectively free.