Stromberg Carlson Rotary Desktop, Please help identify a feature

[rogersrr]

Hello All,
I am new to this forum and was wondering if someone out there might be able to help me identify this phone model and it's strange feature. It appears to me to be a 500 series but it has a switch on the lower left side and the hand written dial tag says l=phone and -=carrier. Can anyone out there please help me with what I have here. Any help would be greatly appreciated.

Thanks in advance,
Richard

[paul-f]

Welcome, Richard!

What markings are on the bottom of the phone?

Chances are good that the switch was originally intended to switch between two lines, and may have been simply labeled or perhaps modified for a particular purpose.

SC and others made 500-series sets under license from Western Electric, so the WE part numbers may have been used.

Check out some of the model numbers including the 510 and 515 in the charts here:
  http://www.paul-f.com/we500typ.htm

[rogersrr]

Thanks for your reply. I will check that link out. There are no markings on the bottom except for "FINAL INSPECTION AUG 1974 40" and loud. No other tags or numbers anywhere. On the handset it does say Stromberg Carlson S-C G3.

[rogersrr]

This couple of pics of the inside might help