If you have two phones with extension 1234. When you type in 1234 for TAPS, it cannot pull one unique record. If on one of those lines,external phone mask is 97281XXXX and on the other it is 46934XXXX. Now when you type 972811234 when prompted to dial extension with external phone mask, TAPS can pull out a unique record from the DB. But if external phone mask on both the phones for the shared line is same, then TAPS will not get a unique record even after external phone mask is used.
Use a (X) wildcard in the external phone number mask
Configure the External Number Mask as a Mask
Line A : 919392xxxx
Line B : 919392xxxx