Oki Telephony Adapter - Manual (Page 21)

13 Placing Calls
Details of services
There are two ways to use the VoIP-TA unit; using both a PSTN line and
the IP network or using only the IP network. These services are
determined by the data setup.
Using both a PSTN line and the IP network
Line selection
The selection of a PSTN line or IP network is specified by the first digit of
the phone number set by the Maintenance Console Software. Please follow
the instructions provided by your network manager.
Third party incoming call during another call
For PSTN line receiving services using hookflash (hooking) from
regional telephone service company.
• Response to incoming calls from a PSTN line during a telephone
call using the IP network.