My UK HTC Chacha phone running 2.3.5 since the last few months shows a notification since the last couple of days that there is a software update available. But the menu only says that it's a bit over 7MB to downloads, it doesn't specify what software update this is which version -- how to find out the details?
The ChaCha does the actual updates check by contacting some webservers (*.htc.com) which are listed in build.prop. All released ROM updates are listed at http://forum.xda-developers.com/showthread.php?t=2094100 but with a 7MB download it must be something else.
The over 7MB to download part could be that the phone is set in a way that downloading files >7Mb would require a Wi-Fi connection.
To avoid data wastage many phones have this feature to enable warning/limit downloads over the mobile data usage. This settings can be managed under the settings options of your Mobile Data option.
Just by un-checking the option you can easily download the update OTA