supposedly it is both sent and received combined. However I find that the devices usage status can very from what AT&T shows. Also the usage statistics under settings shows your usage since the last time you went in and reset it yourself. So if you have had it for more than one month you have used 257mb recieved in total since you have had the device.
With a normal phone account you can log on to the ATT website and view your data usage or even send a text message to get your data usage status. But with the iPad there really is no way that I have found to get the current months data usage except calling them up on the phone and asking.
You may want to go under cellular data in settings and check to make sure you are signed up for the 250MB plan. ATT is supposed to give you a warning message when you get close to the end of your 250MB plan.