Send message to phone

Hi guys,
what i need to do is to send messages thru wifi from a computer to a mobile phone based on the ip of the mobile device, is there a way to do it?

What kind of messages?

just need to send a brief text message to Users that are getting intó my wireless network without authorization. just to scare them

You can't send SMS messages or "Text messages" without the phone number.

But, the bigger problem is that people are using your wireless without your permission. You should check into that.

Use good passwords,. dont use WEP,. you know, just basic security stuff and you should be good.