Less younger Smokey,
Both the distance/time length (close to 200nm), route and altitude of the a/c, and intelligibility of the reception make cellular as the cause of "interference" a no-go.
At first glance, and if the "dial tones" were actually dialing tones (DTMF), I could suggest so-called "long range telephones" which are indeed widely used in that part of the world.
These mid- to high power "telephones" are actually full duplex radios (10 to 50W and more), operating in the 30-50MHz bands, which in "hot" regions can provide communications over very long distances (especially early morning and early evening), talking several hundreds of miles here.
In many cases it is a point-to-point (private) radio network, i.e. a private wireless telephone network, with or without an interconnection to the regular public telephone.
I could well imagine a timber company linking its HQ with its remote locations.
The worst harmonic is usually the 3rd one.... 44.6 x 3 = guess what