I live in Europe.
First of all - the networks were not built after the technology was mature. We REPLACED the old network (NMT) with a newer network (GSM) which has been steadily evolving since then (3G, 4G). The 4G is basically a new network again, but as the phones are backwards compatible, the coverage is not such a big issue - if 4G stations cannot be reached, the phone uses 3G or older stations seamlessly.
Also - socialism or regulation is not the root cause. I think the root cause is that all our networks use the same standard and you have always been able to slap your SIM card into any phone you buy since 1995 or so. At the same time US phones were tied to a carrier - they did not work in another network - therefore you bought your phone from your carrier. In Europe you always bought your phone from an electronics shop and SIM from a carrier.
The main regulatory trick that further fueled competition was when you could switch networks without changing your number. After that the competition went insane and prices went clise to zero. I pay for "unlimited" data (they start to cap speeds at some point if you torrent with it which i don't know exactly as i haven't hit the trigger) and calls by the minute - which amounts to around 6-7euros a month ($8-9ish). Paying 40-60$ a month sounds like a pure insanity - my mobile bills were that high in the nineties.