Content and User Management Solution

A client of mine has approached me wanting database management for his website.

He is after users to be able to sign up to input and update there own details.

He is also wanting the the ability to manage his database (content and user wise) and send info out to his clients either via email or SMS, depending on what they have choosen as there preferred contact method.

For the website I was thinking of using an Open Source CMS written in PHP or ASP. I was hoping that some of the CMS may have modules built in to have the ability to send SMS or atleast be able to hook into another service that sends SMS via the web.

Any suggestions would be greatly appreciated. As always when I use an open source solution on a commercial level I donate a % of the job to the developers or their community.
So if you are writing one let me know and you could get some dollars...