It seems to be the case with any gym to get that. I've been on a few taster days or similar and I think one must have rang about once and left a voice message, but another must have continued bombarding me with calls and texts for about 6 months. Of course, the aim of these weekends etc is to gain customers, so it is understandble, just some go overboard it seems. So, I'll agree with that.
Do not give them your real phone number, you will get far too many text messages with offers from them, the messages cannot be blocked by the phone or the network!