Hi, I just installed to latest Ubuntu Phone build of version 15.04 (r24) on my Nexus 4 (came via Update notification in the phone itself, i.e. didn't need to flash-update the phone via desktop) =d> Aparently some work has been done on the bluetooth part of the OS.
Anyway, before that update (with 15.04 (r23)) I wasn't able to connnect or even find the handsfree set built into my Toyota Auris at all. Now, however, at least the handshake (pairing) seems to work: The Nexus 4 finds the infotainment system as a bluetooth device (of type headset or something similar) and offers to exchang a pin to pair the phone with the device. Likewise the Toyota Touch 2 System displays a message asking whether the pin is displayed on the mobile phone.
Unfortunately after the pairing, when the system actually tries to "automatically" open a bluetooth connection, it fails. I've tried switching the auto-connect switch in the bluetooth settings of Ubuntu Phone on and off, and also hit the "Connect" button several times but to no avail.
There have been some older articles regarding Toyota Touch claiming not all bluetooth protocols for all phones had been implemented on the infotainment system, yet. However when I tried another Nexus with android installed the pairing AND the actual connection workd instantly, so it's not the phone (hardware) nor Toyota Touch 2 that's causing the problem.
I'll give it one more shot and try to find a software update for the infotainment system and see if that helps, but my guess it I'll need to wait until r25 of 15.04 or so to get some more parts of the bluetooth protocol(s) implemented :-k. I wish I could be of any help there, but while being actually a programmer, I don't have any experience with driver implemetation or other such "hardware-focused" software.