It seems that Twilio requires the number you are sending the SMS to, to be registered with the Twiliio console. I am looking for a service that will allow me to dynamically send a text message to a user’s phone number without requiring pre-registration with a 3rd party service. Any suggestions?
So, you misunderstand. Twilio API can send to whatever number you need. What you have to have is a Twilio phone number from which those messages will be sent. This is a small (but not insignificant) extra cost.
There are other services that can use a shared, rotating phone number as the source for your text messages (and, like Twilio, you can acquire a dedicated number if you desire).
For example, ClickSend.
(I use ClickSend for my grupz.com app, and use the ClickSend SMS Bubble plugin for that and it works great. ClickSend also has really reasonable pricing in terms of cost-per-text.
I also have a Twilio phone number just for yucks for doing and testing other things, but don’t use it in any of my production apps. I think I acquired a Twilio phone number so I could play around with their robocalling API which is pretty cool. Their demo API call for that is hilarious.)