Twilio fell 6.6 percent into the closing bell, though shares pared losses after hours.
Amazon's Pinpoint lets app managers "determine which push notifications to send, decide when to deliver the notifications, and track the results of your campaign." (It's worth noting that AWS has had SMS texting capability through its Simple Notification Service since 2011.)
"This is a continuation of our technology partnership with Amazon. Two-way SMS is another capability being utilized by Amazon Pinpoint as part of our existing relationship," said a Twilio spokesperson.
Twilio CEO Jeff Lawson, who used to work at Amazon, said in a tweet that he's "excited that Twilio is now helping to power engagement on @AWS Pinpoint."
Twilio was heralded as one of the major IPOs of 2016 when it went public. But, despite some strong quarterly earnings reports, shares have fallen more than 57 percent over the past 12 months, as the company lowered its revenue expectations after its largest customer, Uber, said it would change the way it handled in-app communications, according to Drexel Hamilton analyst Brian White.