Will a new logic board fix my in-call audio problems?

Recently, I've entirely lost the ability to hear the voice or sound from a caller on the other side of the line. Similarly, the caller cannot hear any sound during the call. The call goes through but, basically, one cannot hear anything from the other during the call. The speakers and microphone are fully functional in other applications like skype and voice-record. After taking it to several people to analyze, I was told that the motherboard was dysfunctional and that the only resolution would be a new phone (it fell pretty badly a while ago and it has been a typical problem associated with falls.)

1. If I buy a new motherboard for the iPhone 4 from eBay, can I simply install it and the problem would be fixed?

2. Will the motherboard come preloaded with all the iPhone functions?

3. Will it conflict with the IMEI (as in will I have to do something to make sure I get a particular motherboard)?

4. What would a new motherboard do to the phone? Will it just be like a new unlocked phone? Will it have everything preset like when I first purchased the phone or will I have to program it?

5. Anything else I need to know before buying and changing the motherboard

Thank you and I'm sorry for the many questions!