As I understand it - In the beginning any company selling mail order was supposed to charge sales tax, or you were supposed to voluntarily pay it when you file taxes (yeah, right). Internet sales were exempted to help the internet companies grow. That time is over. Now they are just like everyone else. The exemptions were allowed to expire by Congress so the states can demand sales tax.
Again, as I understand it, Telephone sales were always taxable, and are definitely taxable now.
The big thing is enforcement. How does the state of New York force a vendor in Idaho to pay New York taxes? Some companies may try to run under the radar and not charge tax, but that's a dangerous thing to do as the buyer may become liable for the taxes.
States get really nasty about tax money for some reason -