To put phone calls on air when you cant afford a hybrid here is a
cheap effective solution.Take the incoming audio into your mixer in
from a connection directly ACROSS the ear piece of the phone
handset.While not any where as effective as a hybrid this method
makes use of the "anti-sidetone circuitry within the phone to reduce
the local handset mic into its earpiece and give a resonable on air
balance between incoming and outgoing speech.
Quality is passable and for this after several tests I recommend
using an old "pert" phone as the quality of the balanced armature
magnetic mic is quite good.It can be used succesfully on air during
a phone call with the studio mic off but I use still a little level
inserted fro the studio mic to balance out the sound a little.
Worth a try!