How ADSL screws up your calls.
This is due to the fact that most broadband connections are asynchronous. What this means is that your download and upload rate are vastly disproportionate.
For example, in my office in the heart of Melbourne CBD, I get 10 mb/s down and only 0.7 mb/s up. If I was using DSL as opposed to asynchronous DSL I should be getting 10/10.
If you don't have dedicated line like this it is probably costing you sales without you noticing it. People will be asking you to repeat yourself or in severe cases won't be able to hear you at all. You may think you aren't speaking clearly or your headset is buggy, but it's your connection.
The worst is when you are calling a cellphone over an ADSL connection due to the usual GSM latency as well as your lack of bandwidth, a weird silence of 1 second or so follows, you interrupt your prospect, piss them off and they don't want to talk to you because they think you aren't listening.
Note that you usually can hear the the other person fine, because that's determined by your downstream, but they won't be able to hear you because of the lack of upstream bandwidth.
In a moment of decision the best thing you can do is the right thing. The worst thing you can do is nothing. ~ Theodore Roosevelt