Message's to be send from Asp.net Web Application to Mobile

Question

Dear Friends,
Me and my team members are developing a Multi-level marketing software (MLM). there is a requirement like, when the user's gets registered through the Software a Message should be gone with the (Username & Password) to their Mobile's, by which they can use it and Login next time(in software).
please help me in my Query.This is Web Application.

Thanks & Regards,
Aamir