Why can't I swap the OS in my phone for another one?

That has been the question running on my mind for so long. I use a HP desktop at work, currently running Windows XP SP2. But I know that, if I want, Linux could be made to run on it with minimal efforts (which involve scouting for drivers).  At home, I run around with a Pavilion DV2000 that came with a Vista but I kicked that out and ran XP SP3 for about 5 months before laying my hands on Windows 7 Ultimate evaluation version(which is as sexy as it gets).

If I so desire, I can run some geeky UNIX variants on the same laptop (unfortunately, I’m not a geek so that wouldn’t happen!). Even Apple, the holy grail of closed system, can dual-boot Windows using BootCamp.

The same can’t be said for any of the smart phones in town today. The laziest smart phone today is probably faster and better than the first PC I ever used (Compaq Pressario. Windows 95, 16MB Ram, 800MB Hard disk) but I I still don’t get that degree of flexibility.

I am waiting for that day when I can swap my Symbian for Windows Mobile. Or WebOS for Android.