Hmm, I believe it is a credit limit, and not credit. Basically means if you haven't paid your bill one month, you'll still be able to use your service because you haven't gone over the "credit limit". Going above gets me barred until I pay my bills.

That said, I always get 80% and 100% SMS on my main pack, not my credit. If I have the 10GB pack, I get an SMS when I'm at 8GB and another when I'm at 10GB, after which I could just top up using a data scratch card if I want, or just pay out of bundle charges of 0.1QR / mb. Plus, why don't you just reset the data counter on the device every month? It shows your data usage right below the network logo :)