私话

zhè shì zán men liǎ de sī huà duì bié rén kě yī gè zì yě bù néng shuō

这是咱们俩的私话，对别人可一个字也不能说。

This is just between us. Don't breathe a word to anyone else.

gào sù wǒ sī huà hào mǎ yǒu kòng wǒ dǎ gěi nǐ

告诉我私话号码，有空我打给你。

Tell me your private phone number, and I'll call you when I'm free.