These effects could be provided by the handset or by in-line filtering of the call by the phone service provider. I believe that this would provide a 'richer' experience for callers and lead to a whole range of spin-off services.

Naturally, sounds could be added, to provide alibis or excuses. e.g. -

"I won't be in today {sound of vigourous retching, followed by damp squelching noise}"

"I can't hear you, I'm getting a lot of static..."

"I can't talk now we're under heavy bombardment..."

An alternative would be to provide sophisticated filtering.

> "Who is that with you Darling? Can I hear female voices?"

{caller clicks button to engage call filtering}

< "Nope, I'm here in the hotel room on my own..."

< faint noise heard in background - "Baaa.."

< "Damn!"