Buyer beware when you answer your phone. Nothing wrong with letting it go to voicemail, looking at trip, verifying legality, and then returning phone call. Some at the crew desk might say you have 15 minutes or they will place a missed trip on your schedule. They're flat out wrong. Past practice is what's in play and that is closer to 30 min.

Verifying a sc/fsb assignment on last day off is up to you. First make sure you screen shot at 1801 lcl. If you choose to call back to verify a non flying assignment let the scheduler answer then clearly state your name, employee number and that your are verifying your assignment. Then say goodbye and hang up. Don't leave them time to respond with anything else. You fulfilled your obligation.

Or...20-K-7-e interim measure states " reserves will be considered to have been notified at 2400 for FAR117 unless pilot verifies or is successfully contacted prior to 2400."

Regarding telling crew desk you're out of phone range on long call I've had fairly good luck with this. However, this is scheduler specific. If they did try to ding you I would think reasonable actions could be easily defended in the chief pilots office.