How fast does your internet connection need to be to use VOIP with min problems?

I have DSL that 1.5mbs.

Is that fast enought to use VOIP and not run into alot of problems. I know you would have to be worried about both your up and down speeds. I have heard some say VOIP works great while others say that the service drops their calls or that they have poor quality. I am thinking about using VOIP to add an additional phone line to my small business so that I can call out for free as well in the US. Can I rely of the service or should I stick with a traditional land line? Also does anyone know of a cheap landline long distance placn?

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