Very unprofessional. A recruiter reached out to me to schedule a phone screening (for that day). As it was last minute, I gave her my best available times for that day. She never got back to me. I followed up with an email the next day and she mentioned that her previous day was so busy and that she would give me a call during lunchtime. I basically sat around and waited by my phone for two full days because of this. I understand that things come up and positions get filled, but don't tell someone you will call them for an interview if you are not going to follow up. We all have full time jobs and cannot sit around by our phones all day.