Hello and welcome! Your schedule as an attending really depends on what type of practice you join (or start if you want to go it yourself and hang a shingle). Many primary care groups that do not do inpatient medicine have weekends/holidays off. If you have more partners you have more people that can cover when you want to go on vacation. Same goes for proceduralists, if you work for yourself/private group your schedule really depends on the contract you have with the group. If you work for the hospital there’s less, shall we say ‘wiggle room’ when it comes to call. Again it should all be stated up front in your contract. Residency sucks for everyone, it sucks for certain (ahem surgical) specialties more than others. You still rotate through different services, and they have certain schedules. Call really depends on your program. Don’t choose a specialty based on schedule, because really all schedules suck when you don’t enjoy what you’re doing.
Kennymac is correct in that once you match it’s a binding contract, but only for the year. People do change specialties after intern year. It’s not uncommon. Oh, and the testing never stops, there’s an In-service-exam that everyone takes every year of residency (specialty specific), and then boards (written/oral)when you graduate.