To those using the above services, quick note. You might be charged for the service request, so it's best to call 123 directly still if you have the time. I was browsing through my bill when I noted the "service request" charges, of which is probably from these because I have never used them previously.

I noticed an item on my bill stated as "Info request/Content SMS request". This would be in the SMS section of your detailed bill.
As far as I know, I've never replied to any messages from unknown numbers. I've also never got this charge before. I have 2 lines under my account, and the past month my wife was demonstrating to me on both numbers how to check data usage using the automated messages described previously. Sure enough, the charges popped up on my bill which more or less corresponds to how much I requested at rm0.15 per reply.
Yet to clarify with Maxis though, I didn't think too much of it since I never actually bother using the service.

I've never replied to any unknown numbers, as mentioned. I just ignore them, unless they found some way to charge me for sending their spam. And the charged amount corresponds with the Maxis service replies.