You're right that in the past we've told people to forward 5060-5080 and 35000-65000. We are expanding this to 5000-65000 and will be updating all documentation soon.
We've had at least a dozen users with chronic issues that all went away when expanding to this range and will be using it as standard going forward.
One of our primary CLEC partners (Bandwidth.com) recommends this range since it's what their media gateways use for audio.
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