How can u see in the specifications of a switch if u can attach fiber to the switch or what extra module is required.And do u need something extra to support voip?

We are having a discussion about how to best setup our network. We have 19 subnets and are having some questions about it. If we choose for the 3845 router will it support up to 19 (some more is ok to be on the safe side). subnets or do we need to bu...