I can't help you with the telecomuter thing but I can answer some of your questions.
Cable modem is my favorite in SP it is extremly fast. And you can be downloading things while usuing vonage, I know several that have it. If it changes the phone quality it is because the DSL connection is too slow. My friend uses his several hours a day and does not have down time.
As far as the install speed. My experience:
Went to Coral Cable, asked when it could be installed, they said TODAY in 5 hours. 2 hours later they were at my place and asked if they could install, all equip+modem included $75 BZ, no contract.