Smartphone line access fees are monthly charges levied by your cellular provider that allow you to access their network. According to the Federal Communications Commission (FCC), companies can charge these fees to recover the costs incurred by providing access to their networks to make and receive calls.
Access fees have been around for a good while now. Verizon is more transparent about it than others. The newer unlimited plans is where they baked it into the plan to appear you don't have any.
Here is the retired 2017 unlimited plan to prove that point. Plan itself was $110 with $20 access fees. If you had 2 phones on that plan, your base cost was $150. Split that in half and we have $75 -- typical cost for 2 lines on an unlimited plan today.