The 1961 Federal Wire Act is key to interpreting a 2006 law called the Unlawful Internet Gambling Enforcement Act (UIGEA). The UIGEA states that any gambling activity considered to be illegal for interstate telephone lines under the Wire Act would (after 2006) be considered illegal for online activity.
Thus, if interstate sports betting over the phone lines was banned under the Wire Act, then online sports betting over state borders is banned under UIGEA. Any interpretation of online gambling law pivots on which activities were originally banned under the 1961 Wire Act.