Shown below is ATTs replacement for the small 4X8 Norstar by Nortel, a cheap residential grade piece of garbage phone.
This ATT telephone contains space for four lines and intercom dialing between phones. No KSU exists for these phones and things like call transfer and park do not exist inherently in the phones themselves. The phones are a similar concept to the original ATT Comkey KSU-Less system of the late 70s and early 80s, but are not built with carrier grade durability. This type of residential quality phone is meant for a small home office.
These types of phones retail from $150-$200, so these days its probably more practical and money wise to buy a small KSU from Emetrotel or Avaya ($600-$800 range) or an IP Hosted solution to have a much more professional phone and phone system in your business.