BELL TELEPHONE MANUFACTURING Co.
(BTMC) ANTWERP
Telephone No. 2051

2051A - Parallel connection.
2051B - Series connection.

These telephones were also sold in different combinations.  These are called the Model No. 22055.

Wall-Mounted Telephone Set, Pony Type
for private lines (magnetic call and local battery)
N° 22051

This compact telephone is particularly suitable for private lines. It is equipped with a small generator with two magnets providing ample voltage for such installations, and telephone transmission is as good as that of network devices.

22051A
Wall-Mounted Telephone Set No. 2051A with wood-framed cabinet, varnished on the front and varnished on the sides, nickel-plated metal parts for parallel connection.

Including a magneto generator with 2 magnets No. 2020B, a hook switch No. 2042B, a polarised ringer No. 2016M (resistance 1000ohms), induction coil No. 2207A, Delville type transmitter No. 2629A, a watch receiver No. 2669B with a 2-conductor green silk cord No. 2014, a backboard No. 2014D with a battery box for a Clement Leclanché Large model, two Oblong-shaped Leclanché cells, or two cylindrical dry cell batteries (Blue Bell).

Dimensions: 622 x 206 x 190 mm.

22051B
The same arrangement as above but using the Telephone No. 2051B, but for series connection, complete with with polarised ringer No. 2016N (120ohm resistance).

22051C
The same telephone as the No. 22051A, but without the battery box.

Dimensions: 262 x 158 x 155mm.

22051D
The same telephone as the No. 22051B, but without the battery box.

Dimensions: 262 x 158 x 155mm.
 

Taken from the 1910 BTMC Catalogue

No. 22051A or B