Is it possible to connect the MVP210 directly to a PSTN phone line without using a local office PBX system? Can this box be used to provide a remote-office access to a local dialtone?

Yes, this is how most of our customers use our VOIPs. The PSTN connects to the VOIP FXO channel. The remote office could do the same, or hook a phone directly to the VOIP channel, using the FXS. The remote office could then get access to the PSTN local dial tone.