Skylane 182/RG Turbo Skylane/RG
Flight Crew Private; Flight Crew Instrument
Flight Crew Last 90 Days 21; Flight Crew Total 795; Flight Crew Type 795
Communication Breakdown; Time Pressure
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Aircraft; Human Factors; Weather
While on VFR flight plan and using flight following with the Center controller; I requested an IFR clearance from an upcoming intersection to my destination airport as it was forecast to be mountain obscuration in clouds along a future segment of the flight. Center asked if I had an IFR flight plan on file and I confirmed I did not. He stated he could not help; but I could wait until I got to the next Center sector. I confirmed that I would do that as it was VFR. He then contacted me and said to 'CONTACT Radio to file an IFR Flight Plan.' I was surprised at that; but changed frequencies and contacted as instructed. FSS was also surprised when I asked for an IFR flight plan while in the air and suggested I ask ATC. I told him that ATC declined my request and told me to call FSS to file it. Given the fact that there is a delay in transmitting the IFR Flight Plan request to ATC; I had to file for a point farther along the route than preferred; but it appeared to be VFR for a good distance along the route. While finishing with FSS; I heard calls on the guard radio 'My call sign' 'Contact Center.' I immediately changed frequency to Center and reported in. He seemed upset and instructed me to contact Center which I did immediately.Since I have only one VHF radio on this aircraft; I was unable to contact FSS without going off frequency and should have clarified that with the Center controller; 'did I have permission to leave the frequency and for how long?' Or I could have cancelled flight following; but I wanted the advisories to prevent conflict with other air traffic in the area. Apparently I was crossing into another Center sector and he needed to hand me off.My confusion came from the 'order' to CONTACT Radio. When I got an instruction to CONTACT another frequency from ATC; it felt like an 'order.' Obvious communication confusion with use of the terminology 'CONTACT [frequency]'Another point is that I could have filed an IFR flight plan for the later segment before the flight; but it was a training mission and I could not predict the time I would need it to start until after completing the training segment. Next time I'll do that with an estimated time and ask to pick it up while in flight. Lesson learned.
Intending to file an enroute IFR flight plan; the pilot of a Cessna 182 misunderstood instructions from ATC to do so with Flight Service Station as an order to change frequencies.  With only a single radio; this caused a loss of communication with ATC Center.