Interestingly, a Mexican cartel did something very similar for their comms network about 13 years ago (source)
Soldiers seized 167 antennas, more than 150 repeaters and thousands of cellphones and radios that operated on the system. Some of the remote antennas and relay stations were powered with solar panels.
A lot of plastic is polyethylene, but nowhere near all of it. There are plenty of polymers that can break down naturally, mostly polyesters like PLA (which breaks down into lactic acid, the same naturally produced compound that causes muscle soreness after workouts). A lot of work is being put into making PLA have better material properties so it can replace more of the conventional plastics. It's also generally made from corn and can be pretty close to carbon-neutral. So long story short some biodegradable plastics are worse, but some have legitimate applications and are genuinely better than current options.