Deco-tel Personal Telephone with 505A Plug

[JTinSF1]

I purchased a Deco-tel Personal Telephone (rotary) and the through the back is a wire attached to a Bell System 4 Prong 505A Plug. 

I have Comcast at home, and would like to use the phone but do not know the adapter I need.  I can attach the phone to either the cable modem or regular phone jack's already installed in the apartment.  Also, there's only one cord that's attached to the plug, and I'm not sure if that's both the power and switch.

Pics are attached.

Thank you!!!
Jack

[poplar1]

Jack, there are easily installed (if overpriced) adapters available that would not require opening the phone:

http://www.ebay.com/itm/Telephone-Antique-Adapter-4-Prong-to-Modular-Vintage-Cord-Conversion/162000711039

Since this a rotary phone, it may not dial out with Comcast, but should otherwise function.
Not sure what you mean by "power" and "switch." The phone is powered by the telephone line (or Comcast adapter), and does not require any additional power.

[JTinSF1]

Thank you, thank you! 

Didn't realize that the telephone line was also the power line.

[poplar1]

Only 2 wires from the phone company -- or from the Comcast adapter -- are used to connect the phone.

Even though the plug on your Deco-tel has 4 prongs, only the top 2 are used. The 4-prong plug was introduced in about 1931 for phones that in that era needed 4 wires between the phone and a separate bell box,  but the 4-prong configuration remained the Bell System Standard even after only 2 wires were needed.

The 4-prong p!ug was made obsolete with the introduction of the modular jacks used today.
However, for a while, Bell insisted on keeping the 4-prong p!ugs and jacks when customer wanted to move the phones from room to room. The newer mini-modular plugs and jacks, while "user friendly", were not considered robust enough for frequent moves. I suspect your phone may have been from that mid-70s era -- either as a portable phone in an otherwise modular region, or possibly from a city that had not yet "upgraded" to modular.

[oldguy]

916 area code, are you from the Sacramento CA area? I live in Grass Valley CA.