You see it all the time on television: Someone gets arrested and told that they can have only one phone call. They may even demand it, saying it's a basic right. The police resentfully allow them that call, as if this right is somewhere in the Constitution -- even though it was drafted before phones were invented.
So, do you just get one call? Or is this a myth?
It's a myth. The number of calls you can make depends on your location, your actions, the type of crime you're accused of and many other factors. In some cases, you may not be allowed to make a call when you want. In others, you may be given as many calls as you need or desire. Saying it is limited to one, or that you have a right to one, is misleading.
The myth may stem from the fact that you do have a right to an attorney. Presumably, you need some way to get in touch with that attorney after the arrest. You can refuse to answer questions without a lawyer present.
Of course, the myth also stems from those television tropes. Some experts say that the only reason it began is that it was easier to tell the audience that the character got one call than to figure out what they'd really get in that specific situation. It also helped to build some suspense in a drama, or sitcoms used it as a joke when people wasted their phone calls or had other people hang up on them.
It's very important to sort myth from reality when you get arrested so that you know what rights you really have.