Ending a telephone conversation
I really have to go now. We’ll talk sometime.
There’s someone on the other line. I must say good-bye now.
The doorbell is ringing. I’ll call you back.
Can I call you back? Something has come up.
I have to get back to my work. I’ll call again later.
Can we continue this later? My other line is ringing.
I have to get back to work before the boss sees me.
I won’t keep you any longer.
I’ll let you go now*.
* “I’ll let you go now” is a polite way to end a phone conversation, usually used in personal calls. It would be appropriate with business calls, unless you knew the person well and were very comfortable with them.