Instructions: The sentences below contain additional information, such as examples, that should be separated with commas from the main sentence. The text may also include introductory phrases that also require commas. Add commas when needed.

1. A mobile phone also known as a cell phone in North America is a portable telephone that can be used while the user is moving within a telephone service area.
2. During operation a radio frequency link establishes a connection to the switching systems of a mobile phone operator which provides access to the public switched telephone network (PSTN).
3. From 1983 to 2014 worldwide mobile phone subscriptions grew to over seven billion penetrating 100% of the global population and reaching even the bottom of the economic pyramid.
4. Some people may carry more than one mobile phone for different purposes such as business and personal use.
5. In 2014 there were more than seven billion mobile phone subscribers worldwide a number that is expected to increase in the future.

This text is adapted from a Wikipedia article Mobile phone. This text is licensed under the Creative Commons Attribution-Share-Alike License 3.0.