I'm sure they would figure out a way to roll it into your phone bill.

I think it would be a good thing. This sounds harsh but honestly most of the the types of people that are unwilling to pay $1-3 per month for the service are probably the types that don't make the service a better social network.

It would also hopefully disincentivize government agencies and maybe even politicians from using it as a channel of communications since it's more along the lines of a traditional business arrangement and not a "free, TV-like" service.