Hi why does a contact come as unavailable when you try to call them while he is offline?

[iMore Question]

I don't face the same issue with any other contact. Normally when you call an offline contact they still receive the missed call and it still rings or calls from your end.

Please how does this happen?

I am using i-phone 4s and he is using i-phone 6.

Thanks

 

[kch50428]

I've been trying to replicate this... Can't.