A There is often an easy answer to this question, interferance within the house or office, many small appliances may interfere with your cordless phone but we find the main problem with interferance to be other rechargeable devises such as cell phone chagers tools such as reghagreable swrewdrivers  toys using a charger and in December Xmas tree lights cause many problems. As the phone will perform differently dependant on its location and the environment it is operating in.

Eg a cordless phone used on a sports field with give better range than the same cordless used in a warehouse, we do supply repeaters which may be used with some Dect cordless telephones to increase range in warehouse and work environments