Excel formula to separate numbers

[z3r0aCc3Ss]

I have around 800,000 mobile number database. It's in Microsoft Excel.
Every mobile number is on new line.
Every mobile number has country code, specifically, starting with 91.
Some mobile numbers are wrong; they just start with 12, or 59, etc. I want to discard such numbers which do not start with 91.
Is there any way/formula by which I can distinguish/remove the numbers which do not start with 91?

[bad_brain]

have a look here:
http://en.kioskea.net/faq/6261-excel-a- ... fic-values" onclick="window.open(this.href);return false;

[pseudo_opcode]

or get a parsing library in perl or your favourite scripting language and use Regex