A list of their competitors: https://www.quora.com/Who-are-Twilios-competitors.

As a Twilio customer that spends maybe ~$500 /mo i'll look at any alternative that allows me to send meta data or allows some process to have a foreign key allowing me to persist conversations in a sane manner (and I'm currently researching just that).

Twilio also does not have their own network, so competitors like Bandwidth that have their own network will be able to compete on price. That said current Twilio pricing is not prohibitive in our market and thus isn't a factor for us researching alternatives currently.