Although it might be easy to take it for granted in these days of pervasive cellular telephone service, a variety of other communications services are available to the intrepid traveler for use in both local and long-distance needs.
The need to contact another person may range from being able to call the kids in from the playground, assisting the driver of your truck or bus while negotiating a tight parking spot while standing outside for a clearer view, or being able to call for roadside assistance or to locate the best and nearest pub in unfamiliar territory. While no single radio service will satisfy all of these needs with one instrument, being aware of the choices will help identify the proper service and equipment to do the job properly.
Most familiar, and probably least expensive is what we in the States call "Citizens Band" radio. The 40 channel transceivers are ubiquitous, which makes this type of radio a good choice for being able to contact other operators. While it is possible to get everything from a time check to a tow vehicle by calling out on these radios, the frequency is very crowded, prone to severe interference, and not very private. Short range communication, such as between two vehicles traveling together, or between several radios in close proximity is very good. The operating frequency of 27MHz allows the signal to travel quite a distance, which can be both a blessing and a curse. A blessing if you are trying to contact someone who is over the horizon, and a curse because you will also be talking with 200 million other CB radios worldwide. The general demeanor of the CB radio band is loose and usually friendly, like the internet, anything goes and usually does. No license is required to own or operate these radios
For more reliable radio service, consider amateur (Ham) radio service. Available on a variety of frequencies, this service is held to a high standard of performance. Licenses are required, and amateur radio operators tend to police their own behavior. While idle chit-chat is tolerated, it is expected that you surrender the frequency, or at least yield use of it, when other operators request access. Equipment for this service is usually of high quality, and many amateur radio operators build their own. Ham radio offers the distinction of being able to allow communications which are virtually world-wide, due the operating frequencies involved and helpful nature of the majority of operators.
Recently, Personal Radio Service (FRS) has become popular. These medium-cost units deliver clear communications over limited range. Privacy is usually fairly good, but as there are a limited number of frequencies available, you may find that you are sharing a channel with others, particularly in urban areas and at special events which have many attendees.
Most reliable and private over short distances would be licensed business-band radio transceivers. These VHF or UHF radios usually are licensed to only one user per locality, and although it is possible to eavesdrop on conversations through use of a scanner radio, the security of conversations is better than with most other services. Traveling with these radios can be tricky, as itinerate users may have to use alternate frequencies to avoid interfering with the local radio services in the towns that they pass through. Most business-band users will not tolerate interference on "their" frequency, so coordination of channels used is most important.
Nearly all of the radios discussed are available in configurations that allow them to be powered by mains power, 12 volt vehicle batteries, or disposable/rechargeable penlight cells. Many units can enjoy enhanced performance with the use of outside antennas, and all are available as hand-held "walkie-talkie" units.
Whichever radio service you may decide to utilize, be sure to keep your concentration on the road while using them while driving. Many comfortable headset devices are available these days that allow a driver to have hands-free use of a phone or radio, so that safety isn't compromised during the conversation.
As Stephen Hawking said (on a Pink Floyd album) "All we need to do is keep talking..."