A communications system may include a plurality of data storage devices each using at least one of a plurality of different operating protocols, and a plurality of mobile wireless communications devices for accessing the plurality of data storage devices. Each mobile wireless communications device may also use at least one of the plurality of different operating protocols. The system may further include a protocol interface device. In particular, the protocol interface device may include a protocol engine module for communicating with the plurality of data storage devices using respective operating protocols, and 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 plurality of mobile wireless communications devices using each different operating protocol, and at least one common core service module connected to the proxy modules.