I'm not sure, but, like you, I've only heard this technique suggested for RCN. I can personally vouch that it works for RCN. This summer my promotional rate ended, and I called to see if they could offer me anything better than the full rate. At first they told me they couldn't do anything. Later I received a Comcast offer in the mail and called RCN back, threatening to cancel and switch to Comcast. They transfered me to a different department that was happy to offer me the rate I asked for, which was even cheaper than the promotional rate I had had previously.