Will the TSA allow a HTC desire smart phone on an airplane as a carry on?

Yes. A smartphone is not really considered a carry-on item. It's like your wallet or Keys. Something you put into your pockets. However any smartphone and spare batteries should be in your carryon. You cannot check them.

Of course you can bring your smart phone on.
If they didn't allow smart phones on, how would the millions of flyers that use electronic boarding passes on their phones get on the plane?

They DO NOT care about what kind of phone you have. Millions of people travel with smart phones.

You may bring this aboard. See link. Recommend that you stow the cellphone inside your carry-on bag prior to sending it through the x-ray machine.

http://apps.tsa.dhs.gov/mytsa/cib_results.aspx?search=cellphone
(Direct link from http://www.tsa.gov "When I fly can I bring my.." search tool.)

Yes you can keep your cell phone on the plane, people have been doing it for years.

Yes. You can keep your phone

Smartphones are allowed on airplanes.

Yes. Make sure you turn the phone OFF before boarding.