Why do only some of my incoming calls ring?

[iMore Question]

Sometimes my incoming calls ring and sometimes they do not ring and become missed calls or go to voice mail.

 

[HankAZ]

Sometimes my incoming calls ring and sometimes they do not ring and become missed calls or go to voice mail.

Proper forum etiquette says that it's impolite to ask the same question more than one time - especially only 4 minutes apart.

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