Three factors historically facilitated dissatisfaction while simultaneously listening to the telephone and wearing hearing aids: (1) absence of visual cues, (2) the "coupling" between the phone, and (3) the hearing aids and background noise.
Telecoils have been shown to improve some coupling issues, however, loops and telecoils do not always provide superior speech recognition performance. Rate limiting factors associated with telecoils and loops include vent size, acoustic background noise, electromagnetic interference, and telecoil /telephone positioning.
Picou and Ricketts (2011) examined speech recognition using multiple presentation protocols for telephone-based listening communication. Twenty participants (14 male, 6 female) listened to 14 presentations to both ears (bilateral) simultaneously and/ or to one ear (unilaterally) via occluded and non-occluding dome ear tips, using two background noise levels.
Bilateral presentations resulted in significantly improved speech recognition as compared to unilateral presentations, regardless of background noise and regardless of dome type (occluding or non-occluding). However, dome types were a more significant issue with acoustic telephone presentations. Picou and Ricketts note that wireless signal streaming was beneficial as compared to acoustic telephone listening and often resulted in the best performance across all conditions evaluated.
For More Information, References, and Recommendations
Picou EM, Ricketts TA. (2011) Comparison of Wireless and Acoustic Hearing Aid-Based Telephone Listening Strategies. Ear & Hearing 32(2):209-220.