I found this sentence on https://en.wiktionary.org/wiki/%E3%81%84%E3%82%89%E3%81%A3%E3%81%97%E3%82%83%E3%82%8B and it struck me as odd.
Listening to my co-workers (business phone calls) I've noticed that most times they will drop the particle completely and I don't believe that I have ever heard them use 「が」. As a point of reference I would probably say something like 「〇〇さん、いらっしゃいますでしょうか？」.
My question: Is there a semantic difference between using 「は・が」or nothing at all? Also beyond the base semantics are there any connotations to using 〇〇さん「が・は」？