Using Conditional Call Forwarding and Twilio

Conditional call forwarding is a little discussed feature available on practically all major cell phone carriers.   The idea is simple: by entering a brief code, you can instruct your cellphone to forward calls missed calls to an alternate phone number, rather than dumping the caller into your providers voicemail system.  You can forward all calls, all missed calls, or just specific types of missed calls this way.

When combined with a Twilio incoming phone number, this feature allows you to back a cellphone with your own custom voice application.  This allows you to do some interesting things, such as replacing your carrier voicemail system with your own custom design, or redirecting missed calls back to Twilio and having it Dial another number (or set of numbers).

Conditional Call Forward Codes
Function Activate Cancel
Forward All Calls *21*(Phone Number)# ##21#
Foward Busy *67*(Phone Number)# ##67#
Foward No Answer *61*(Phone Number)# ##61#
Forward Out of Reach *62*(Phone Number)# ##62#
All Conditional Forwards *004*(Phone Number)# ##004#

If you’d like more detailed information on these features, check out the wikipedia page or your own cellphone’s manual.