PTT type Bazel (Siemens Miniset 310)

PTT Type Bazel (Siemens Miniset 310)
PTT Type Bazel (Siemens Miniset 310)

This model from the 90s was named after the Swiss capital, Basel. This name was used before by PTT in the mid 80s for a different model. See also this link: PTT type Bazel (Tritel Elm)

PTT did not produce this phone themselves, but brought out an existing model under their own name.
It took me quite a while to find out what the original make and model was. Now I finally cracked it. At first I thought it would be Swiss, as PTT had a tendency to name their phones after cities of the country where the model originated. Not this time, though.
PTT Type Bazel (Siemens Miniset 310)
PTT Type Bazel (Siemens Miniset 310)

I opened it up to find more about it, but there was very little until I looked in the handset and found the name Siemens on the PCB.

It turns out this is a Siemens Miniset 310. The Miniset is a varied range of phone models Siemens made through the years, the 300 series having several versions with different buttons and functions.
I am happy I have solved this riddle.