I just started central station monitoring last month. I have VOIP for my phone service. If I went with phone monitoring or IP monitoring, either way it's over the cable internet line. One cut of the coax and monitoring is gone. So I decided to go with cellular monitoring through my local alarm company. In tests, and two accidental triggers, I've been very impressed. Our phone rang within 15 seconds of the trigger to see if everything was okay.
It cost more for the monitoring and I had to install the unit, but I'm very happy with how well it works.
Kevin