It is now possible to send out SMS from contacts using the newly uploaded SMS package in HEAD.
The SMS package supports sending SMS using URL based gateways like http://www.any-sms.de and others. It is configurable using parameters so you can have multiple instances of SMS, one for each SMS Gateway you are going to us. If an SMS gateway provides multiple gateways itself, you can also specify which gateway you are going to use.
Last but not least the sender phone number can be either given using a default value (in the parameters) or using a contacts attribute like "mobile_phone".
In the future (aka. if a paying client can be found) mass sending of SMS using the contacts message interface should be possible.
The current state of affairs is described briefly at http://cognovis.de/developer/en/using_sms uncluding a quicktime screencast.
If any of you have an idea how I can embed the quicktime movie in the xowiki page, please let me know.