Hello Maverick,
That's a great question. With the current TDA rules, mainly Accepted Action, the calling player could be liable to complete the bet to 30,000. I like the fact that you separate the action from the verbal because the difference could be substantial. Pushing 5000 forward, without saying anything, could save the calling player 25,000.
The floor could rule one of the following two options: The BB must complete the call or surrender his 5000. Or...After the verbal declaration of "call" the BB might be liable to complete the bet to 30,000 if a strict rule is in force.
There are many other factors that could be considered but, in my opinion, the above is what the current rules dictate.
As far as the use of an all-in button, I would say yes, it would make the all-in raise more clear, especially if the dealer controls the all-in button.