Can anyone recommend Antivirus for Exchange 2007, BlackBerry Enterprise 4.1.4 and Cisco Unity 5?

I am currently using symantec corportate for clients. In the past, we didn't install AV on the servers becuase the clients are all protected and emails were being scanned by our relay before they hit our mail server. We didn't have beefy hardware and didn't want the servers bogging down. However, now we need to be *sure* that viruses don't hit any one of those servers...