What does OnSIP do well? Pretty straight-forward administration. It is clear and easy to figure out how to add users, extensions, etc. We have not had any outages since we started using this service. Setting up Conference Bridges is also relatively easy and they can be assigned a 3 digit extension with a 4-digit access code.
What does OnSIP not do well? Is not easy to integrate with other software like Netsuite (we still have not gotten this to work). This would in theory allow us to pull up a customer's information when they called in by interfacing with the Netsuite database.
What do you wish you had known about OnSIP before using? You pay for additional phone numbers but not for additional extensions. This is great as you can assign separate numbers only to people who really need them while most users just receive an extension.
Have you used a competitor to OnSIP? If so, how does it compare? Yes, I have used Cisco Call manager which was set up as an in-house service as opposed to OnSIP which is a cloud service. The greatest difference was experiencing no outages in OnSIP as opposed to Call manager which would experience them from time to time which can leave workers unable to call except from their cellphones until the service comes back up.