which product should choice?

As the phone line plan will renew, our supplier said they've DDI service available which is used T1 line(is it correct?). Then we can have lot of virtural number to instead of extension number for call in. If so, which config will more suitable? (will keep the analog panasonic pbx as previous diagram setting)

In this case , you need a 1 port T1 card and a 4 port FXS card use together. OpenVox part number will be:

D110P 1 port T1/E1 card or D110PG(same feature but ROHS compliant).
A400P40 (4 port FXS card).