Williams Sound, Eden Prairie, MN; 800 843-3544; williamsav.com.
Phonic Ear, Petaluma, CA; 800 227-0735; www.phonicear.com.
Telex, Minneapolis, MN; 612 887-5550; www.telex.com.
Martel Electronics, Placentia, CA; 714 572-0100; www.martelelectronics.com.