Hello, is this John speaking?
喂，是John吗?
Can I talk to John?
请问John在吗?
Hi, John. It's Alice.
您好John,我是Alice.
This is Alice speaking.
我是Alice.
May I have your name , please?
请问您是谁?
Who do you wish to talk to?
您要找谁呀?
Yes , speaking.
是的,我是。
That's me.
我就是。
You're speaking/talking to her.
您正在跟她说话。
This is her.
我就是。(注: 男的用This is him.)