The fix if you're stuck dealing with crappy equipment that has massively oversized buffers is to throttle the connection in another device downstream of the modem to slightly under what the modem will throttle you to and then in addition to that you can also implement QoS so that your VoIP traffic is put into a different queue and give that queue a higher priority.
This is all predicated on the assumption that your ISP is actually providing what they say they are 100% of the time. If you pay for 5 Mbps upstream, set the QoS to 4.5 Mbps and your ISP delivers 4 Mbps 10% of the time then for that 10% of the time your equipment will be sending too fast and you'll go back to filling up that oversized buffer just like before.
You'll probably have to setup two different essids. Most devices I've used will keep using the same ap even when its signal is lousy and they have a great signal to the other ap
I'm now thinking that our occasional VoIP issues probably aren't Time Warner (er, "Spectrum," whatever)'s fault, but might be caused by overwhelming the physical capabilities of our router.
So what sort of hardware should I plead with our CEO to let me purchase? Is there any way I can test, calculate, or prove that upgrading the infrastructure will prevent the operational staff from saying "Hello..? Hello..? Can you hear me?" on a phone call?
It sounds like, from hopping over to the linked CNet article, that maybe putting another router with the same network name and password, hardwired into the opposite corner from the existing router, would let us split the load across the office. But the end of Anand's article says I should throw up my hands and quit because the back room where a new router would go can still hear the original Asus transmitting loud and clear, so client devices would still have delays caused by picking up other networks.