How shall I setup user event notifications in my code?

I'm coding a team collaboration web app in PHP, and I have a few events that users get notified about through email and/or SMS. The current way I'm doing it is as follows:

• Every user has his notification settings in the database as boolean variables.
• Say users would be notified when someone comments on the team's page. When the function that posts a comment is called, the same function would contain extra code that checks "who wants to be notified about this?" and then sends notifications to them (which slows down the function a bit).

Is there a more efficient/faster/flexible way to setup notifications? maybe through a script that runs via a cron job? or shall I just keep doing it this way?

I appreciate your help.

I implemented a similar method to the one you're following on a website with a multi-table approach. The users table held the contact information along with opt-in, opt-out options while an event table held the instructions to notify. Several other events were hard coded because of their importance. The thing that set the site apart a bit was a "workflow" area on the user's dashboard that also showed the user what action items they had. We found that most users ignored the emails and dealt directly with that dashboard workflow area. You'd be surprised how many times people change emails or just ignore them altogether.

With 280,000 users and daily visits in the tens of thousands, there was no performance issue noticed. However, the process of queuing emails can be inefficient if you're not careful, so take particular time to benchmark your mail sending functions--its as easy as echoing out microtime before and after the mail send is accomplished--to evaluate its effectiveness. On my current company's site, such improvements yielded a 800% reduction of email queuing time (queuing being the process of generating the emails and submitting them via php mailer to the mail system for distribution)