No problem, Rajan, Let me explain.

When the phone you’re dailing is busy, you will hear:

“nin bo da de dian hua zheng zai tong hua zhong, qing shao hou zai bo”

Which means: the number you dailed is busy now, please dail later.

If it’s because of network problem, you will hear:

“nin bo da de dian hua xian zai wu fa jie tong, qing shao hou zai bo”

which means: the number you dailed cannot be put through, please dail later.

If the phone is turned off, then you will hear:

“nin bo da de dian hua yi guan ji, qing shao hou zai bo”

which means: the number you dailed is power off, please dail later.

In above sentences:

nin bo da de dian hua = the number you dailed

zheng zai tong hua = is busy now

wu fa jie tong = nextwork problem

guan ji = power off

ting ji = out of service

qing shao hou zai bo = please dail later

I hope this helps!