A communications system may include data storage devices each using at least one of a plurality of different operating protocols, and mobile wireless communications devices (MWCDs) for accessing the data storage devices and each using at least one of the different operating protocols. The system may further include a protocol interface device, which may include a protocol engine module for communicating with the data storage devices using respective operating protocols. The protocol interface device may further include a front-end proxy module coupled to the protocol engine. The front-end proxy module may include a respective proxy module for communicating with the MWCDs using each different operating protocol. The front-end proxy module may also include one or more common core service modules coupled to the proxy modules and communicating therewith at a first layer, and communicating with the protocol engine module at a second layer lower than the first layer.