Language complainers like William Safire and Richard Lederer often complain about the misuse of 'which' and 'that'. In school I learned the standard SAT usage of these two terms, and it made complete sense to me, because in my dialect you just didn't use these terms the way some people do. Linguists who observe the way the English language really works (as opposed to how Safire and Lederer want it to work) point out that the so-called misuse is not a misuse. It's a normal part of the English language. Arnold Zwicky even claims that virtually everyone uses 'which' in exactly the ways the style manuals say not to, including the writers of those manuals.
Well, I want to say that there is something bad about this normal part of the English language. It is a stylistic issue, and it's one that conveys something about the speaker. It's not grammatically wrong. It does sound uppity, though. In my dialect, you would never say "hand me the phone which is on the table" unless you wanted to sound like a snob. You might say "hand me the phone that's on the table". You might say, "The phone, which is on the table, is not plugged in." You wouldn't really even use 'that' unless you needed it. "Hand me the phone on the table" is much better than either, but the one with 'that' sounds ok. The one with 'which' just sounds like the kind of thing you'd expect someone with lots of money and private tutors to say.