How to add "..." to a long sentence?

Question

Possible Duplicates:
How to get first x chars from a string, without cutting off the last word?
Truncate a multibyte String to n chars

Follow is a type of title:

$title = "On the way to mexico city";

For display purpose the title can be approximately 10-20 characters long. So the above should be converted to something like:

"On the way to..."

Similarly, the following:

"My confirmation form"

should become

"My confirmation..."

"My confir..." wouldn't make sense

What's the best way to do this?