Aiight, here's the thing, the idea of a blue box doesn't work anymore, the original tone based phone systems ran by using specific signals, 2600 was the frequency at which the phone would grab a line opened, (hence the name of the web site and quarterly publishing, which I surprisingly found a book store that carried it, didn't realize anyone in the US carried that thing) and the buttons on the phone would make different tones to identify which was being pushed.
Now, the newer phones in the US run on a dual signal, meaning you have to get a blue box that oscillates between 2 different signals at once (nearly impossible to make a portable version of) since the signals have to happen at the exact same time, making one is extremely difficult since it would have to be 2 blue boxes running on 2 different frequencies.
Honestly I'd just look into building one of the old ones and framing it, besides, it'd be cheaper just to use the current price, I mean honestly, would you really spend like $50 for all the research, burned out parts, screw ups, etc. necessary to make a phone call ?