Telemarketing will not teach you good sales skills as it applies to business. The reason being that telemarketers are taught to be pushy and to continuously/quickly talk to convince people to buy their products. But, if you're cold calling businesses to offer them something, you need to have the opposite skill set.
You need to listen more than you talk and you need to avoid being pushy, because people naturally back away from pushy salesmen. They want to feel like they're making the decision on their own, and not being pressured into it.