)Edit 1/22/2016: Got an email from the manufacturer this morning, offering to replace the broken parts, free of charge. It works with whatsapp calling. The hardware that came was designed for 4 mounts on the wall, but only 2 grooves were premilled. 90? ma meritano ogni centesimo speso spedizioni Amazon sempre al top This should give you an idea of the durability of these slippers. Easy to build All in all, a great value, it works, its inexpensive and well made. I was happy I dont have to buy two sets of devices for the same purpose. They do not produce sound. So far they have performed admirably and I cannot recommend them enough.