In the U.S., regulations permit CW operations throughout the amateur bands. That makes the phone section of a band look tempting when the CW/digital part of the band is busy with a contest. I wonder if my friends and I can reasonably have our scheduled QSO in the phone part of the band when the CW/digital part is busy.
Since we are talking about the United States, the "phone" portions of each band are actually described as phone, CW & image. So it's not only legal, but it's perfectly acceptable to operate CW in that portion of the band.
Contest rules generally confine contesters to the CW-only portion of the band making the rest of the band a viable option during CW or Digital only contests.
As for good operating practices, they are the same as always: find a clear spot, listen, ask if the frequency is in use, listen, commence operation. Some bands, notably 40m and 80m have some long standing scheduled nets, you'll want to avoid those, otherwise you should be OK. CW takes so little bandwidth, it's pretty easy to slide past a CW QSO if you are looking for room to operate SSB.
Probably you will want to avoid contest style operation though to avoid causing any misunderstandings. A normal rag-chew style QSO will likely not bother anyone.
