I was with Verizon since the early 2000's in Network Engineering Roles, I did not leave by my choice. I won't have the order exactly right, but here goes:
MCI acquisition Verizon, bought them and did nothing to grow the assets, at least in the South. 18 years later, Verizon wrote down 5.8 billion. Some of the environment changed, a lot of it was Verizon. Verizon kept the MCI and Wireless engineering teams separate, they did not mix for 10 years it seems. One Fiber project was supposed to fix that, but too little too late.
iPhone, Verizon let ATT negotiate an exclusive deal on the iPhone. ATT had massive capacity issues after the iPhone launched, but customers left Verizon in droves to get the iPhone. Verizon lost out because of a Verizon splash screen on the phone!? Along with that was the LG Chocolate and Blackberry Storm. Verizon lied to us all saying these were iPhone killers, not even a flesh wound.
ATT FirstNet deal, whatever the terms of that was, ATT has a superior First Responder network because of it. This is consistent monthly revenue and loyalty. They got money and used it to upgrade the towers.
Sprint. Verizon should have bought them. While TMobile was launching sprint's 2.5ghz WiMax spectrum as quickly as they could, Verizon was trying to catch TMobile by overbidding on C-band because Millimeter wave spectrum was all but worthless.
Marnie Walden - in her desire to be the most powerful woman in wireless, she sc--wed Verizon Royally. She was the force behind "Go90", "Oath", and the AOL and Yahoo acquisitions. She bailed when they named Vestberg, but the damage was done.
Verizon bought companies for a tiny bit of IP, then shut them down.
Verizon bought Vessel (YouTube competitor) Intel OnCue, Edge Cast Networks, Yahoo Answered and either shut them or shut them down in 2 years. Verizon also partnered with RedBox for a streaming service that lasted 1.5 years. 26 million for 18-19 months. Brilliant.
More recently, Verizon threw away Nokia gear and went to Samsung in roughly 46% of the country. Additionally the C-band Rollout was salt and pepper. TMobile was building 2.5ghz 5G sites before the ink was dry, Verizon started AFTER the deal was closed, they did little to no prep work.
Long term, Verizon underestimated TMobile. We used to laugh at them, their bare-bones cell sites, their lack of engineers in the field, their pre-paid customer base. Look where they are now.
One more thing, Verizon su-ks at negotiating and writing contracts and brokering deals. iPhone, FirstNet, Fiber Franchises, you name it. Verizon tends to su-k at it.
Two stiff points of competition working against Verizon: ATT's fiber right-of-way and knowledge around that process helped them build sites plus they had more mature processes around Turf vendors that spilled over to tower and small cell leases and procedures.
TMobile was supposed to be acquired by ATT, but when that failed they had a roughly 4-6 billion penalty to be paid by ATT if the deal failed for any reason. ATT paid them 3 billion in cash. This skyrocketed TMO's network build. They put that money straight into Network engineering and it showed.
I thought I was done, but Verizon decimated the NOC, the NOC engineers were sharp women and men that needed a stepping stone and were eager and hungry to learn and do better. Now they barely answer the phone or call out on an outage.
Then there is just the waste. I saw on more than one occasion massive equipment was decommissioned without ever being powered or integrated. As good as engineers were at Verizon, there were some that had no reason to be there, a front-line engineer III was going to the gym with the director of network?! Was he there to be a personal trainer or an engineer? But wait, there's more, but I wont go into that.
I don't wish anything bad for Verizon, but they have been self-effacing their own business and profits for a long, long time.