NEC MobilePro 880 - Manual (Page 108)

Setting Up a Remote Connection 5-3
Connecting the Internal Modem
Follow these steps to connect an RJ-11 telephone cable to the
internal modem.
1. Locate the modem cover on the right side of the NEC
MobilePro and open it.
2. Carefully plug the RJ-11 telephone cable into the modem
connector.
Connecting the telephone cable