Well, this is an interesting question. Essentially there are two answers Cellphone/no cellphone pilots. If you Have a cellphone then be somewhere reasonably close to your terminal. Those that say "on airport property" are just leading you to trouble. Pretty sure if You just head out to the lookout spot at DFW and claim you are on airport property it's not going to fly. I doubt you would win that grievance, but hey give it a shot and let me know how it goes.

If you do not have/forgot your cell phone then you need to be in the crew room or quiet room. They have(should) phones where they can call you. If you need a meal break just advise CS and tell them you will be back in 30-40 minutes.

Don't worry about rushing off to the plane as soon as they call you. There is no time limit you have to be there by. Just get your things and head over there. If you are eating then advise CS you are going to finish your food and then head over there. If they call you at lunch time and you haven't eaten then get some food before you get there and advise CS you are taking a meal break. Just don't be that guy that deliberately tries to make it delayed because you think you are sticking it to the man. You aren't.