I like to start with something like, "Wouldn't dream of calling you at this hour except I knew you'd want to be aware that (Mrs. Patient's BP is 210/130, O2 sats are 70%, whatever) She's our x-year-old patient admitted Tuesday for (brief rundown just in case this doc has no clue who Mrs. Patient is.) We've already (whatever interventions have been tried) with no luck. I'm sure open for suggestions

."
It acknowledges the suckiness of having to call him/her at that hour (and I know they're being paid a lot of money and they knew what they were getting into in med school, but they're human and any human deserves a little courtesy at that hour

.) Also gives them a second to wake up. And I always thank them, again out of common courtesy.