Hi,
This sounds like a REN problem - ringer equivalency number. If you have too many analog phones (generally in the US more than 5) on the same line they may not ring, or may have ring issues. Even if you have only one phone on the line, but it is a long distance from the device trying to ring it you can have the same issue. I have seen this in large plants where it is a long run of copper to the phone (in my case through several buildings). Additionally if there are intermediate devices you can have issues with this as well. Please note that even though they don't ring, in most other cases - as you describe- they may work just fine.
Here are the ring related specs from the VG224 data sheet:
Ring Voltage | 50Vrms into 5 REN at zero loop length (balanced) if no DC offset | 54Vrms into 5 REN at zero loop length (balanced) if no DC offset |
Ring Frequency | 20, 25, 30, 50 Hz | 20, 25, 30, 50 Hz |
Ring Waveform | Sine wave if no DC offset 20V and 24V DC offset will be trapezoidal | Sine wave up to 35V DC offset |
Ring Load | 5REN with no DC offset 2REN with DC offset | 5REN with no DC offset 2REN with DC offset |
REN Loading | 5 REN/port, 12 REN/system (maximum) | 5 REN/port, 12 REN/system (maximum) |