Hi everyone sorry if this is a basic question, having trouble understanding the Cisco website.  We have Cisco 7960 IP phones and one 7970 that we have used for years with Asterisk, all flashed to SIP.  We are looking at purchasing a UC540 system to use now instead and from what I understand these phones work with it. 

We were most likely going to buy a bunch of SPA504G IP phones to use with it instead but might not if I can just use the phones I have.  The only thing is when flashed as SIP these phones seem to lack a lot of features, like you can't customize the soft keys and so on.  I was just wondering if they have to be in SIP to work with the UC540 or if they can be flashed back to SCCP and be used with it?  From what I know they need Cisco Call Manager to manage them and their settings in SCCP but I don't see anything about that mentioned with the UC540 just about it's CCA application so not sure if that would do the same thing.

Functionality wise am I gaining/losing anything by keeping these phones or is it better to switch them?  Thanks so much!