@apost02 I think right now, in 16.04, bluetooth headsets only work for streaming media. The HFP/HSP mode is not supported by the version of pulseaudio in 16.04 with the version of bluez in 16.04. It seems to only support A2DP streaming.
I don't think there is any way to work around these issues currently. Hopefully we can get newer versions of both included at some point, but it's a fair amount of work.
Perhaps your issue may be considered a separate bug to this. Please open an issue on https://github.com/ubports/ubuntu-touch/issues if one does not already exist for your problem.