Consider the Panasonic KX-TGP550 SIP DECT.

http://www.amazon.com/Panasonic-KX-TGP550-SIP-DECT-Phone/dp/B002SUEQBY/ref=sr_1_3?s=office-products&ie=UTF8&qid=1451685963&sr=1-3&keywords=panasonic+sip

Supports up to six phones and eight lines. Can do everything you want except for record calls. I think there are other means available to record calls.