A communications system may include a plurality of data storage devices for storing data using at least one of a plurality of different operating protocols. The system may further include a plurality of mobile wireless communications devices for accessing the data storage devices and each using at least one of the plurality of different operating protocols. Moreover, a protocol interface device may also be included. The protocol interface device may include a front-end proxy module for communicating with the plurality of mobile wireless communications devices using respective operating protocols, and a protocol engine module communicating with the front-end proxy module using a common interface protocol. The protocol interface device may also include a respective interface connector module for translating communications between the protocol engine module and the plurality of data storage devices for each of the different operating protocols.