Well, they're not doing voice so Twilio still has that advantage. Also, support is likely to be much better with a startup than with the huge behemoth.
However, Amazon has the footprint to get you worldwide delivery. Twilio just arrived in (parts of) the EU, but that's a temporary advantage. Also, there's that 0.75c charge. That's already a 0.25% saving and Amazon have a habit of reducing the price whenever possible.
Twilio et al will likely focus on better service, more features, easier signup and use.
However, Amazon has the footprint to get you worldwide delivery. Twilio just arrived in (parts of) the EU, but that's a temporary advantage. Also, there's that 0.75c charge. That's already a 0.25% saving and Amazon have a habit of reducing the price whenever possible.
Twilio et al will likely focus on better service, more features, easier signup and use.