https://www.twilio.com/labs/twimlets
I use the "Forward" one for calls.
For SMS, it used to be not too complicated - I would host a file directly on Twilio (using a Twilio bin) to forward the SMS to another number.
Recently, sending out SMS's has become a lot more complicated due to compliance (Twilio wants to make sure you don't spam people - but the burden on small developers was just too much for me, after ~2-3 months of back and forth emailing with them to get approved)
I've switched my SMS forwarding to use https://pushover.net/ . I use Twilio's hosted nodejs platform to get the incoming SMS message, and use Pushover's API.
It's potentially brittle-ish overall (lots of pieces) but it's also been working for years.
A native mobile app that would let me just get calls and sms for my hosted Twilio phone numbers is really what I'm asking for... :-)
In some countries even phone carriers may offer SIP trunking for individuals. But most often they work with a handful of resellers, who in turn have smaller and smaller companies as their clients. So, if you only need to support a small volume of calls you'd find that your prices per connection or per minute are higher.
Similar to sending email, telephony is a business of volume. The more call you make the less your prices are going to be. I worked in telephony space for a few years, and it's a fascinating industry.
Up until the latest AI wave, Twilio was almost in every thread about a new service!
