I was an intern at GigaOM in 2009 (a popular tech blog that ran conferences), and my first memory of Twilio was going to the sales people and trying to convince them to give Twilio a discounted booth because I thought the product was so great. I remember the salesperson laughing and saying "this booth costs more money than they have in their bank account", but there was some extra inventory and we got them the booth.
The early people all just had this vibe of technical-but-not-complicated. It's common now, but at the time it was such a breath of fresh air. They were one of the first companies to pitch "easy of use" (compared to "look at how amazingly complex we are!"). I know this is super obvious now, but back then I had never felt anything like that.
All the people I met (I specifically remember Danielle) were friendly and excited... not in a sales-y way, but in a "I just love what we're doing and want you to, too" way. And again, I know this doesn't feel unique now, but that's because Twilio helped shape how we think about all of this.
I loved their attitude, such as this talk from John Sheehan (https://www.heavybit.com/library/video/runscope-ceo-and-twil...) about how they look at customers. I remember him saying they would fly to any little city that would have them and buy pizza and just hang out. They caught on early that there were so many tech people out there around the country who would become lifelong supporters because of little gestures like this.
Overall, a lot of what I can say about Twilio is super obvious now. But it's kinda like how people watch Friends for the first time in 2023 and say "meh it's a pretty generic sitcom". It's because they created the whole genre and shifted how everything thinks.