Max, yes you CAN pair the two, even though everyone says it's not possible. First, configure the phone -- ALL contacts must be stored on the SIM card, rather than phone memory. The phone will usually store contact to "memory" by default... you'll have to swap them to the SIM card in the "contacts" list. Also, the telephone numbers have to be entered with the "1" preceding the number. Sync won't recognize the entries, without that format. Ok, once you have that completed, the phone is ready. Now, go into the "phone" settings in the Sync system and delete ALL info from the previous phone, including the contact list #phonebook#. Then, switch on the Bluetooth on the LG840...the Sync system should walk you through the pairing process and then ask if you want to "download phonebook". Tell it "yes". After that, you should be good to go. Mine works as well as it did with the Galaxy S3 that was previously connected. I hope this helps!!
You know, one would think that 'Bluetooth' operating specs. would be the same from device to device. As you have found there are problems. Could be as simple as a wire bundle shielding the rec. antenna port or simply, will not work. If the reception port is visible is there a 'film' of protection over the trim somewhere that is still in place. (this for wireless). For plugin, it isn't impossible for small mini harness to be defective. Try another. I hope any of this helps. Good Luck. ( i am trained in 2-way Radio Communications)