I recently (temporarily) switched from high-speed cable to DSL. The local cable companies do not service my present address. I've been using VOIP (Voice-over-IP) phones for the longest time without issue. I recently upgraded my phone system and on ADSL the voice quality is horrible.
I suspect the reason for this is that the local phone company doesn't want you to use VOIP because if you do, then you're not paying for their local phone service. Additionally, they're likely trying to filter any attempts at people streaming any content from their local networks. To combat this, by default in most of the DSL modems the phone companies, by default, have configured network communications to work with UBR (Unspecified bit rate), which means that the line variably bursts with a *potential* high-speed of your maximum internet speed.
For Voice-Over-IP communications the setting would need to be CBR (Constant bit rate) since you're streaming audio over the internet. So for anyone considering using Vonage or Magic Jack on a DSL system, you're probably better off paying your local monopoly to have a POTS (Plain Old Telephone System)... until of course they upgrade your circuit to fiber.
