$249.96 would be the total BEFORE tax for the 5 lines. $130.00 for first line and $29.99 for each secondary line (x4)=$119.96. The premium plan includes unlimited MBs for web browsing/email, VCast Video, VZ Navigator, Mobile Email subscription and unlimited messaging for everyone. None of the applications use additional airtime.
Keep in mind you don't have to get all your lines premium, you can bump it down to just $9.99 and that line will still receive unlimited messaging. So it can be pretty flexible.
So yes, you're looking at $250 + tax after all is said and done.
Hope this helps.
So to simplify that, you will not be charged additional airtime if you have this plan.