From HiPBX Wiki

A (highly recommended) option for the Astribanks is the TCO - Telco Connector Option

Unfortunately, documentation on this is quite hard to find. By reverse engineering the cable, I've discovered the pinouts and how they map to each port.

You can use this information to make your own cables, or, you can buy a pre-made cable directly from QLD VoIP Services.

Front Port	TCO Pair	Telco A	Telco B
A1	44/64	1/26
A2	43/63	2/27
A3	42/62	3/28
A4	41/61	4/29
A5	40/60	5/30
A6	69/50	6/31
A7	73/54	7/32
A8	17/37	8/33
B1	8/28	9/34
B2	7/27	10/35
B3	6/26	11/36
B4	5/25	12/37
B5	4/24	13/38
B6	3/23	14/39
B7	2/22	15/40
B8	1/21	16/41
C1	52/72		1/26
C2	51/71		2/27
C3	38/18		3/28
C4	19/39		4/29
C5	48/68		5/30
C6	47/67		6/31
C7	66/45		7/32
C8	45/65		8/33
D1	16/36		9/34
D2	15/35		10/35
D3	14/34		11/36
D4	13/33		12/37
D5	12/32		13/38
D6	11/31		14/39
D7	10/30		15/40
D8	9/29		16/41

Note that the table above splits into two 16 port Telco cables. This is the common cabling layout for larger PABXs. If you're replacing a smaller PABX that is using all 24 ports of the Telco cable, you'll need to change the wiring around yourself. Note that QLD VoIP also sells a 24 port cable, along with the 2 x 16 in the link above.