I don't screen I just have my phone off, during lessons. I don't take phone calls when I am working with a horse or a rider. I don't work 8-5 hours. On average at the end of my day I will have 6-10 messages 3 will be for horse related things. My day ends between 8-10pm, starts between 11am-1pm. I still have to cook meals for my husband and take care of all the animals and keep the house in order. It is a very busy day. I am not making excuses I am just saying this is what I have to do.
I do return phone calls but I can normally only get one in that night if it's not too late. And I take the most pressing call and get back to them. The next day depending on schedule I will get them in as soon as I can. But I am down right busy. I normally get everyone's messages returned with in a week, generally within two days and generally all at once. I get a break I sit down and I will be on the phone for 4 hours returning calls.
Those people who know me really well don't call me but email me. I am up late at nights and return emails daily it is much easier for me. I get stuck in a lot of what I call 'the horse chats' Horse people love to talk about horses I am no exclusion. But when I am in a hurry and I have someone on the phone asking me 101 question about how I would interpret this behavior or how do I get them to do this. It can be frustrating too say the least. You don't get paid for the time you spend on the phone and a lot of people take advantage of that. (I am not saying everyone does)
See if there is any other way you can get a hold of them, maybe they are like me and emailing is the best option.