Since this afternoon the ringtone on our landline is intermittent.
I have checked the settings and tested the ringtones, they work fine in the settings and the problem is happening on other handsets and the base station ringer, so I have ruled out the speakers on these devices.
Since on the internal tests the ringtones work, the only difference is that the calls are coming from an outside line. I have also rang the landline from several mobile phones with same results.
I have ran the VM landline test on your website and it says the tests run were "inconclusive".
My thinking is that the signal that triggers the phone to ring on the landline is intermittent and this is being reflected by the speakers on the handsets/base station.
There has been work on a sunken drain cover along the street today, it occurred to us that maybe it has interfered with the landline. Our internet and TV services are fine.
The ringtone is back to normal. The workers have almost finished the access cover relevelling (it's not a drain cover, I couldn't think of the right word yesterday) so it may have been related to their work on the pavement. It is near to where VM cabling runs, hence the theory.
Once the work is totally finished it will hopefully be the end of the matter.