These field telephones are Bundeswehr surplus. These would be paired with a radio operator inside the command element of a unit. Unless you have a Bundeswehr radio or an appropriate converter, you probably won't be able to get it working.
The Short & Sweet:
- Genuine Bundeswehr surplus field phone
- Made in the 1970s and 1980s
- Comes with carrying strap for field use, may be vinyl or canvas
- Not compatible with modern radio jacks
- Sold as a novelty item