Since you're mailing the errors already, you might just send out one extra mail to an sms provider. I use http://www.clickatell.com/ for this.
I just filter all the mails I receive with procmail and if certain errors occur I forward the message to a mailbox at clickatell. It will send me an sms to notify me.
Anyway, there are much better ways of doing this, but this is a very low effort way of implementing this :)
Thanks a lot for the tip, sounds pretty nice, I will check it out.