A C560 Crew reported a pressurization control problem prevented pressurizing the aircraft after takeoff. The Captain decided to divert to an enroute airport but was unable to contact his Company as required by SOP so he landed exercised Captain's authority and landed.

Narrative

After departing we had a problem with the pressurization. The cabin immediately climbed at 6000ft/min then settled and then descended at 3000ft/min. We completed the departure; leveled at 6000' and advised ATC that we would not be going any higher and requested to stay on course until we were able to advise them of where we wanted to go to divert. I tried without any success to contact the Company on the flight phone; AFIS and ARINC. I wasn't able to get a hold of Company Dispatch or Flight Manager. We waited for almost 20 minutes before I decided that I would divert and land to get a hold of the company and further assist our passenger all the while keeping them calm and assured that the situation was under control. We landed without incident and were able to get the owner on another flight to his destination. We did not declare an emergency; as I did not believe that the safety of the passengers and aircraft were ever at risk. I realize that I am required by Company policy to be in contact with the Company before any decision to divert is made; however; I was forced into a situation that made me make a command decision because I had no other possible means to communicate with the Company. I had already exhausted all the options that I could try to communicate with the Company and I believed it was time for me to make the decision to land and not further exacerbate an already bad situation and wait for an answer that may never come. I believe that we should have reliable NEW flight phones that use current digital technology and an AFIS system that doesn't take longer than the pony express to deliver a message to the company. I further believe that there should be an emergency AFIS address that goes straight to someone who can make a response instead of hoping that someone will see my message sometime soon.