How it works
Verizon codes come from Verizon’s call forwarding FAQs; T-Mobile codes from its self-service short codes page. Carriers can change codes, so test after setting them. Full details, troubleshooting and the iPhone Live Voicemail fix are in the call forwarding codes guide.
Frequently asked questions
Does this work for AT&T?
AT&T's wireless support pages set up forwarding through your phone's settings rather than publishing dial codes, so this tool shows those steps for AT&T instead.
Why isn't conditional forwarding working on my iPhone?
iPhone's Live Voicemail can answer missed calls before the network forwards them. Apple suggests turning Live Voicemail off if carrier conditional forwarding isn't working.