aaapriceVEC TRX-20 Telephone Call Recording adapter with 3 ft. cord and 3.5mm plug.

Will this work with an Avaya digital phone?

Can this be used while using the speaker option on a landline phone?

Would it be possible to put the plug into an audio-out jack of an MP3 player and play a message that could be heard through the phone handset?

Can you use this on cordless landline phone?