There is no way to do this currently - the forum alerts are only via email.
Thanks for the suggestion though, we will consider it for future enhancements!
The SUN forum isn`t completely homegrown. Long time ago in a galaxy far away, it started out as a WebWiz Forum. At this point it`s very heavily modded and so it made more sense for us to keep working with the existing system rather than migrate to a completely new one.
On a side note, vBulletin is a PHP/mySQL application and so doesn`t mesh well with the Microsoft-based platform that StartupNation is built on.