The first telephone address books had a simple memory function for numbers that were assigned to a button. The amount of memory and the number of possible entries was very limited. More modern handsets had address books in larger, non-volatile memories, which could be edited and easily accessed via a menu. With the advent of mobile phones the opportunity came to store address books directly to the SIM card. This offers the advantage that when changing the mobile phone, but keeping the SIM card, the address book is transferred and does not have to be re-entered. Modern smartphones allow their users to save the address book, together with extensive information about each contact, directly on the device itself or in the cloud. Cloud address books allow users to access their contacts with any device. The address books are synchronised automatically over the Internet.
The advent of the cloud PBX and Computer Telephony Integration (CTI) has seen the telephone and computer merge ever closer together. Modern systems can establish telephone calls with just the click of a mouse from a link in an email program. With incoming calls, the extensive additional information can be displayed on the computer screen. This allows, for example, the person making the call to have access to their entire telephone history or to see customer records, also from other departments, such as purchase orders or complaints. This simplifies telephone use, making communication within the company more efficient.