Can you attach a loud ringing bell to a SPA504 and if so which ones?

how many levels within the one auto attendant on the UC320?

Will the Plantronics S11 and Plantronics CS55 work on the SPA504 and SPA508 phones?

How many directory entries does the UC320 hold and how many directory entries do the SPA 504 and 508 phones hold

Please advise the best headset for the SPA phones we have sold Plantronics C555 with the lifter and cusotmers are not happy with them on the SPA phones, please suggest a goodwireless headset.Thanks