I saw this product at Globalspec.  It combines 5 Ethernet ports with a telephone modem.

SIXNET's ET-5MS-MDM is a 5 Port Remote Access Switch that combines an industrial telephone modem with an industrial Ethernet managed switch, allows the user to access an Ethernet network from any remote location over standard telephone lines.

From the Globalspec news item:

The ET-5MS-MDM was designed to be rugged, reliable, real-time and secure.

• Rugged: The ruggedness comes from its wide operating temperature range, industrial ratings (UL, CE, marine, hazloc, etc.) plus SIXNET's 25+ years of expertise in designing truly industrial rated products.
• Reliable: The reliability is field proven with over 1,000,000 service-free hours (MTBF) based on real-world data of thousands of switches currently in the field.
• Real-Time: The real-time operation is possible due to SIXNET's open Linux software that supports advanced networking functions such as SNMP, RSTP, QoS, VLAN, IGMP and much more.
• Secure: Plus, there is real security using HTTPS, SSH, SNMPv3, password protection and authentication.