Are you actually USING that many minutes a month? And is that 280 your average montly bill, or are you a new customer and that's bill #1 rec'd? I can see it at that high if you're on an unlimited talk family plan, I guess, but if you aren't coming anywhere close to those minutes, and that's the plan you're on, drop it down and save some change.
For example, my gf and I have 3 lines on ours, all smartphones, on the 700 min T&T plan, and our bill isn't that high for all three. And between all three, we use maybe 400 minutes a month.
And if it's just cause you just signed up, then the prorate and activation fees (if applicable) are naturally going to raise the first bill. That should be no surprise.