How does internal wiring affect eSpeed?

eSpeed is provided through telephone lines going to the house. Most houses have one telephone line going inside the house from the distribution pole outside. It is then a common practice to have many parallel lines to accommodate practical usage of the telephones at home.
However, having too many parallel lines decrease the overall broadband bandwidth and affect the broadband connection. Common symptoms for this would be:

•Slow connection to the Internet
•Disconnected while browsing the Internet
•Other phone sets emits a loud buzzing noise when used