To date nothing or essentially ignore a bomb threat. Someone who wants to plant a bomb and kill people will not call it in or warn anyone.

...dealing with such calls was part of the training everyone received - such as cutting all power to the store, shutting the registers, and so on.

I think it's more a case of better safe than sorry. You don't want to ignore something that could hurt someone then be that one time where it's true - it'd be lawsuit city then.

on the TVEE! So it must be true in real life right? They can't put anything on TVEE that is not true. I read that on the Internets.

This is the most recent example I can find:

http://www.irishtimes.com/news/crime-and-law/bomb-left-in-belfast-could-have-caused-carnage-psni-warns-1.2198320

It seems counter intuitive for a bomber to give a warning, but there are several reasons a warning may be given. The bomber could have second thoughts after placing a bomb and not want to return, or it could be that multiple parties are involved and one isn't fully on board to they give a warning.

Years ago there was a bomb threat phoned in for a flight I was about to take. They towed the plane to a distant runway, spread the luggage out on the tarmac and ferried us out there one by one and had us unpack our bags in the presence of several heavily armed men with dogs. Another team with dogs searched the plane. When that was done they loaded us up and we flew. There was never an announcement about whether or not a bomb was found and I never heard/read any news about it later in spite of going out of my way to search for information.

happened in Northern Ireland with the I.R.A., although my memory about this may be faulty. Certainly your observation about the pointlessness of doing this makes a lot of sense.

Someone mentioned an example of that above.

If there was one, I figured it would be the IRA or perhaps a South American rebel group targeting military or police in particular, rather than a mass terror attack for the terror value per se.

And some left wing radicals here in the 60s and 70s.

Took place at an abortion clinic; person called about a bomb inside the building, people evacuated and
police/fire were called, bomb was actually outside the building when detonated.

IIRC, the method was borrowed from the IRA (if you can't get the bomb to the people... get the people to the bomb).

I'm thinking the information taken in the phone call shouldn't even be written down. Maybe even hang up on the caller when a possible bombing is mentioned.