I use Plivo to forward calls and sms for 2 of my old phone numbers. One is a US # and one is Canadian #. You don't have to program it to forward, you could very easily code an autoresponder type thing.

Here's some code to get you started: https://github.com/dannysu/plivo-forward-ruby

I also used Twilio and Anveo before. Both of those should work too.