Incoming calls are going straight to voicemail. How do I get it to ring?

SOURCE: phone doesn't ring on incoming calls

i cannot fix the number of times for the ringer on my vetch phoneset

SOURCE: PHONES WILL NOT RING ON

This question was posted on the troubleshooting page for the VT-9118. This answer is specific to this model.
The VT-9118 can use one of 4 different ring tones, and can be turned off. 

To reset your ring tone: 

1. Remove the handset from the base. 
2. Press PROG. You should hear a single short beep.
3. Press #.  You should hear a single short beep. 
4. Press a number 1 through 4. You should hear a long "ring" tone (it might be startling!). You can try other numbers from 1 to 4 to hear them all.  
5. Press MEM to confirm your ring. You will hear a medium beep.