Your so called savings by using Obi is a crock. There is no savings when hours of your time is wasted trying to get it to work.
I sympathize with your frustration and feel sorry that some other users on the forums here are being mean while they happily call away on their working Obi devices.
Obi seems to be one of those things that gets rave reviews because either the overwhelming majority are lucky and don't have issues or they are network engineers and can and don't mind fiddling around with settings. If you fall into the small percentage of users who have real problems though and you're not a network engineer, good luck!
But as the poster above me suggested, maybe your router is the problem. Why not post the exact model number of your router? If it's your router model that's the problem there will be numerous reports about it not being compatible with VOIP devices. Let's find out if that's the issue.