VoIP and Alarm Monitoring
Alarm signals do not communicate reliably when sent over the network of a 3rd party VoIP service provider. Remove the provider from the equation and it is perfectly reliable to use "off the shelf" Linksys VoIP equipment for communication with the Virtual Monitoring Platform.
Why your alarm fails to work using VoIP
A VoIP service provider has control over the network settings (namely the audio codec) between your VoIP adapter and the number you are calling. Understandably, the VoIP provider only cares about providing crystal clear human voice for their customers. Unfortunately, they do not care about alarm monitoring, and it just so happens that many of the technologies used in providing clear human voice have a deteremental affect on alarm signal transmission.
When the VoIP service provider is taken out of the equation, what you are left with is a "raw" Internet connection. Using Linksys VoIP equipment at the protected premises and a software based Virtual Receiver at the Monitoring Center, in effect you have your own private network - a "controlled" path to the Monitoring Center. Even though the data still travels over the public internet, you have full control of the optimisation technologies and you can adjust them to suit how an alarm panel and alarm receiver are designed to work - not a human voice.

VoIP servers are not reliable
Another very important reason to remove the VoIP service provider from the equation is that they become another link in the chain between your alarm panel and the Monitoring Center. VoIP service providers are well known for taking their servers down for routine maintenance and it is not uncommon for them to be offline for days at a time. Many have only a single server, meaning there is no redundancy in place for when things go wrong.
In summary, using "off the shelf" Linksys VoIP equipment that is provisioned for alarm monitoring as opposed to human voice, it is reliable to send alarms over the Internet.