OT, I know ...

We have rarely, if ever, received SMS messages on our landline phone
until now. Son's school have started sending updates by that method,
which is OK, but is there any possibility we will be charged for using
the service?

Whilst I'm confident the school service is OK, I don't know who the
caller is until accepting the message. What concerns me is accepting
something that is not from the school, and somehow being conned. Is
that possible?
--
Graeme