Other thing you can look at too:
1. Had any storms lately?
2. Is the fixed telephone making any crackling noises?
3. Are you sure the line Filters are connected/or connected correctly?
4. Some modems don't like the modem power brick connected to a power board
5. Make sure no other electrical equipment is interfering with the modern
6. Make sure the modern isn't over heating
You could go on for ever
The first two require Telstra to fix, If you hear crackling or other voices on the line call Telstra and report a fault for the Phone (if she has one) they will check the line