Do yourself a favor - Buy Mind Blasters by Peter Duffie, and look up Stephen Jones' 1812. This is an ingenious method of forcing any large number you need, and is simple and direct. It can be easily adapted to your 6-digit phone number, and also to postal codes, years (he demonstrates the method by forcing the year 1812), and more!

It can also be repeated with different results, if need be.

I just realized, Corona, that I didn't describe what the audience would see if you use the 1812 approach.

Without giving too much away, several spectators choose random numbers, and decide how the digits from those random numbers are to be arranged in an equation. You then have an impartial party add up all the numbers (generated by the audience!) involved on a calculator, and the answer is the phone number you're forcing (depending on the desired phone number itself, the equation would consist of either five 5-digit numbers, or six 6-digit numbers).

You would have to keep the process of creating each 5- or 6-digit number interesting, and pace the effect well, for this to work.

Just yesterday I happened to once again watch the Harry Allen "Comedy Bits & Magic Routines" Volume #2 (from L&L Publishing - I've no benefit from promoting them). The Calculator Prediction effect is explained on the DVD. Very simple, very direct and you can force up to the total number of digits that the calculator will allow. It's done with any generic "scientific" calculator, and indeed can be borrowed.

Also, a friend here in Las Vegas has gimmicked other "non-scientific" calculators for me by taking the back off the unit and switching some wires. Not sure exactly how he does it, but if you'd like his contact information, PM me.