Phone is the term used for the type of radio communication that involves talking and listening. This is the old talk into the mic, listen to the speaker type of radio communications. There are three basic types of phone communications used, based on their type of radio modulation used.
FM (frequency modulation) is what you hear on 2 meters when using a handheld and working through the club repeater. It is the mode where most hams begin. FM has exceptional quality for voice communication and there is generally no noise or fading that you hear on HF with SSB or CW. However because of its wide bandwidth requirements it is usually limited to bands such as 2m(VHF) or 70cm(UHF) where there is lots of room. Some FM can also be heard on the upper portion of the 10 meters band around 29 MHz, where it is also permitted. But its not allowed on any other HF Band.
AM (amplitude modulation) was the early mode used by hams for voice transmission. In AM the signal is a carrier (like CW) that has upper and lower sidebands that are modulated by varying the amplitude (strength) of the signal. Most shortwave broadcast stations use this method. If you tune to the BBC or some such station using either USB or LSB on your receiver you can hear the carrier as a continuous tone as you move slightly away from the center of the signal. If you listen around the upper end of the 80 meter band you may find some hams using this mode. However AM takes twice the bandwidth of SSB and so is not widely used in Amateur radio. It is used among people who like to collect older radios and those that just love the sound of AM which is said to be much fuller, richer and warmer than SSB.
SSB (single sideband) is a mode where the carrier and one sideband of the AM mode has been suppressed. Whether using USB (upper sideband) or LSB (lower sideband) more of the transmitter's signal is focused on powering just the one single sideband used as compared to AM which has to divide the transmitting energy between both sidebands and a carrier. This can give SSB an almost 300-400% more efficient use of transmission power compared to AM. As a result the SSB signal travels much farther and is easier to copy under many unfavorable conditions. This makes SSB is the phone mode of choice for Amateurs on the HF bands.
Phone has replaced CW/Morse Code as the most popular method of radio communications over the years, and its now used on nearly every band.
Amateur radio operators use their amateur radio station to make contacts with individual hams as well as participating in round table discussion groups or "rag chew sessions" on the air. Some join in regularly scheduled on-air meetings with other amateur radio operators, called "nets" (as in "networks") which are moderated by a station referred to as "Net Control". Nets can allow operators to learn procedures for emergencies, be an informal round table or be topical, covering specific interests shared by a group.
Nets operate more or less formally depending on their purpose and organization. Groups of nets may organize and operate in collaboration for a common purpose, such as to pass along emergency messages in time of disaster. One such system of nets is the National Traffic System (NTS), organized and operated by members of the American Radio Relay League (ARRL) to handle routine and emergency messages on a nationwide and local basis.
Traffic nets operate primarily to relay written messages. For decades, amateur radio operators passed both routine and emergency messages on behalf of others as part of its public-service mission. Outside of times of emergency, traffic nets are largely used for training purposes. During emergencies (such as natural disasters) – especially when normal communications channels are disabled or compromised – traffic nets (utilizing emergency-powered stations) are used to pass information into and out of affected areas.
DX nets are organized to help amateur radio operators make contact with stations in distant locations or regions where amateur radio operators are scarce. By checking into a DX net, a ham could have a chance to contact another station he or she might otherwise not be likely to hear by randomly tuning across the amateur bands. There are nets for both international contacts and also for those who are trying to collect all the US states, and earn their "worked all states" award.
Amateur radio clubs often organize nets to foster communication between members on a regular basis. These can be clubs based on geographic location or clubs formed around a special interest. These are most often held on local repeaters. The ARTS Club has a weekly net on the W4CN Repeater.
Special interest clubs or non-club groups often organize nets to enable discussions on a particular topic. A wide variety of such nets are in operation. One such example is nets that meet to discuss vintage or antique radio equipment. Another example is nets for using and discussing the AM mode of voice transmission. There are also nets for veterans, various political topics, swap-meets, as well as women and youth nets.
Here are some links for more information about Nets: