Some instructions say hold Volume Down + Power 5 seconds to open the boot menu. On a ChaCha with software version 126.96.36.199 opens the boot menu immediately; I just hold Volume Down and get the boot menu within a second.
Booting works differently depending on which Android and ROM version you have. Open Settings, About this phone, Software and add in your question which version you have. On another ChaCha with software version 1.54.401.3 I get re reaction at all with holding Volume Down, but maybe the button is physically broken.
So 2.3.3, and presumably original ROM installed?
HTC did release updates from Android 2.3.3 to 2.3.5 -- see https://en.wikipedia.org/wiki/HTC_ChaCha
Which phones got that update was supposedly Carrier-specific. I've seen mixed info on forums and official. On 12th June 2014 I tried (manually) to access the update servers listed in the ChaCha device props files (the ones used for OTA = Over The Air/half-automatic updates), and it is possible that OTA no longer works for ChaCha.
(I've seen the Facebook button start making trouble, and that slows down the phone to almost unusable levels -- and then it needs either repair or if you install a ROM that ignores the Facebook share button.)