From the Independent this morning there was a piece in Extra about the use of  Modern Etiquette by J.H.M. Walsh.
Classics such as:

Under what circumstances do you answer a ringing mobile phone?

1) While walking, provided you're by yourself and at least 10 metres from any passer-by.
2) At an informal lunch with business collagues who are boring you to death.
3) When shipwrecked (it might be a lifeboat).
Otherwise, it is dead naff to be summoned, like a servant, by a ringing noise.

Under what circumstances do you absolutely not ever answer a ringing mobile phone?

1) While proposing marriage in the Savoy Grill.
2) While speaking at a memorial service in St. Martin-in-the-Fields.
3) While negotiating a loan over £250,000
4) While interviewing Madonna/ President Bush/ the Queen/ Pope Benedict VXI.
5) While enjoying am intimate moment with anyone over the age of 35.