I agree with Fuji's sentiments entirely. If they want you to phone this should be explicitly stated. Otherwise PPR means by any means eg, radio, light signals or whatever.
Actually Gengis's suggestion is a good one too. But I do wish that airfields only put PPR if they really wanted it. At most airfields where you phone up becuase it says PPR by telephone even, half of them wondr why you are phoning.
Someone mentioned the case of airfields abroad, specifically Germany where "outside hours" the airfield doesnt exist. This is an unfortunate thing in Germany, but exactly the opposite in France, when "outside hours" is when everyone flies! Except for specific airfields that are listed as restricted use, you can land anywhere and if no one answers you on the radio, you just make standard no radio position calls and land. Pity its not the same in the UK. We do have a number of airfields like this, others where you can operate "out of hours" with prior permission (usually in writing, sometimes just a phonecall) and others where you cant even do that- sometime for planning restrictions.
Of course in the USA everywhere is open all the time and they've never heard of PPR. If its closed then there are Xs on the runways and its NOTAMed closed. Which for the case of someones 747 engine runs should also be the case!
Unless there really are good reasons why PPR is required due to restrictions , or a private strip, I cant see any reason why most airfields are adopting these bureaucratic procedures.
Worse was the case of one airfield a few years ago which insisted on PPR by Telephone. As I was flying from Wiltshire to Scotland via Barton, I was not sure if Id have enough fuel to quite make Barton depending on the winds. So the day before, when planning my flight I phoned up for PPR, told them I might be coming around 3pm if necessary and got my prior permission. As it happened on the day, I had a tailwind, so could make it to Barton easily non stop. Fuelled up there and then continued to Carlisle for a nightstop. got to Carlisle who told me that D+D were looking for me!!! Wonder what that is about! I hadnt filed a flightplan. so called them up from the tower. Apparently this airfield had reported me overdue as I hadnt got there at my PPR time, that Id booked the day before saying I might come!! So they wasted D+D's time as well as no doubt other airfield's time who had been phoned up. If I had wanted that type of service, obviously I would have filed a flightplan. If I'd have been able to just come in if I needed to without PPR by phone, then I could have done that if necessary and saved all the bother. It would seem that this airfield is really taking it all a bit too far!
The rule really should be that if the windsock is flying and runway not Xed then the airfield is open, unless specifically Notamed otherwise.