When is a warrantless arrest applicable for using a telephone for betting purposes?

A warrantless arrest is generally permissible under the Fourth Amendment when there is probable cause to believe that a crime is being committed. In the context of using a telephone for betting purposes, an officer's presence at the scene is significant because it allows them to directly observe the activity taking place. This immediate presence creates an opportunity for the officer to corroborate their suspicions and ensures that they can make a more informed judgment about whether a crime is occurring.

When officers are on the scene and witness behavior that suggests illegal betting is taking place, they may have enough probable cause for a warrantless arrest. This principle is grounded in the need for officers to act swiftly to prevent the further commission of a crime or to secure evidence that could be lost if they were to obtain a warrant first.

The other scenarios presented, such as making a call to a known location, involving multiple participants, or a recorded call, do not inherently provide the same level of immediate observation and probable cause for an officer to act without a warrant.