I have the Ooma hub, my 2Wire Integrated Modem/Wireless Router and my cordless phone base on the same desk within 18 inches of each other.
The wireless connection, as well as other home appliances can interfere with a cordless phone base unit. The cordless Dect 6.0 phones we are using sound even better than the 5.8 phones we were using with the base unit plugged into the Ooma hub.
If you have quality problems with your Ooma, I would start with your phones first to make sure they aren't the culprit. Ideally, I would try a non-cordless phone direct into the hub and check the quality. If it sounds good, your older cordless phone system could be the problem.