Can I unroot my phone?

Don't think so. I think thats how you brick your phone

 

When you unroot, you replace everything in the memory with what the carrier shipped, just like you’re opening the box again. And of course, root-level files cannot be touched if you’re unrooted – that’s why you rooted in the first place.

You can’t have it both ways. I mean really...

 

Yeah what people above said. And really....why would you wanna unroot it? What's the point ?

 

We saw such a request over in the Desire forum a while back. In that case the member had a specific need to have an unrooted phone (corporate network security insisted on it IIRC), though there are also a few apps which won't run on rooted phones (and of course many that won't run without root!). There's more to it than just uninstalling the superuser app, unfortunately - it's really a question for the ROM developer, as I'm pretty sure it would require a rebuild of the ROM.