I'm sure they will use this as a negotiating tool against the union, but that doesn't make the financial hit they're going to take any less real. Their financial statements have to account for what they think their future obligations are going to cost them. If they lose some subsidies, or end up having to pitch in more to fund a retiree health care plan that will be hit with new taxes come 2018, then those obligations will cost them more and they're required to adjust their financials accordingly.
Now it's fair game to question whether or not in AT&T's case that hit really does equate to $1B dollars. Like evay said earlier in the thread, this is a good time to take a writeoff. But there's definitely going to be some kind of hit for companies when the government starts taking subsidies and/or tax breaks away.