Answering machines became more widely used after the restructuring of AT&T in 1984, which was when the machines became affordable and sales reached one million units per year in the US. The first post-breakup device went by the trade name of DuoPhone and was sold by Tandy (Radio Shack). This device and its successors were designed by Sava Jacobson, an electrical engineer with a private consulting business. While early answering machines used magnetic tape technology, most modern equipment uses solid state memory storage; some devices use a combination of both, with a solid-state circuit for the outgoing message and a cassette for the incoming messages.