The Barry Diller-backed Aereo service, which allows users to watch broadcast TV shows on mobile devices like the iPad and iPhone or on their personal computers, announced a new subscription plan on Monday. Subscribers willing to pay an additional $4 a month (on top of the $8 they currently pay) will be able to record up to 60 hours of programs with the device versus 20 hours that they now receive free. At the same time the company is doing away with its $1-a-day plan and also ending its annual membership rate of $80. Currently Aereo is only available in the greater New York City area, but is due to be introduced in Boston this week. The television networks have launched a thus-far-unsuccessful legal attempt to block it.