Great answers, Donay.
I would just like to add that to me "Hold on a minute" sounds very informal, and I would not use it if I worked in a formal setting, say for example, for a lawyer or doctor's office.
How may I help you is more polite and formal than "How can I help you."
You will often hear, "How may I direct your call?"
"Whom would you like to speak to" is more formal than "Who would you like to speak to."
Similarly, "To whom would you like to speak?"http://grammar.quickanddirtytips.com/who-versus-whom.aspx
The receptionist will often say:
"Please hold while I transfer your call."