Samsung S4 motherboard damaged. The problem started during system upgrade that failed and caused a reboot loop (constant restart and shutdown, repeated infinitely). There wasn't any chance of getting the contact list backed up. The only alternative was to factory reset the device. Tried it and didn't work. Submitted the phone to Samsung Service Center at Plaza Singapore. Do you know that there are four Samsung service centers in Singapore?
The service staff was robotic. She talked robot-like with "Sir" added to the end of the sentence. The usual, "if phone found tampered, dropped, etc. then it voids warranty). I said I understood. At the end of the session, I submitted an electronic feedback as "excellent". The electronic tablet for feedback was placed right in front of the service staff for him/her to see and I wouldn't want to demoralize her by giving mediocre rating (it sorta defeat the purpose, right?).
The repair was swift, it took three days to get the phone repaired. The notice for collection was sent to my other number via SMS. At the counter, while I was there to collect the phone, I asked what was wrong with the phone and the staff said that they had changed the motherboard. I asked how long is the warranty for the motherboard. The staff said that the warranty is the same as the remainder of the phone warranty, i.e. few months time, which translate to mean that there isn't any warranty. I asked if the motherboard issue was frequent for S4. He said it's case-by-case (meaning, "I don't know"). Anyway, I was glad that the phone is available for use.
What I was not glad was the contact I had on this phone was gone forever. I should remember to backup my contacts regularly in the future.