Probably more common outside the first world at some of the 3rd rate airlines out there. At my foreign carrier, it's rare (and not very smart) for a pilot to give the contracted 3 month notice.

The reason is that the carrier will not pay your last paycheck(s). So, generally, you quietly get a job elsewhere, and then the day you get paid, you hop on a plane to your new job.

Some pilots here don't even bother with a phone call or email. On average, one or two per week leave.