A mobile phone is an electronic device that can receive and make calls over a wireless network.
Generally speaking a telephone is a wired phone which has certain limitation in use. You cannot carry the telephone along with you, outside your home or office. Consider if the same telephone is connected wirelessly, then you have the facility of carrying it outside your home or office. Now to carry this telephone it should be handy and portable. Hence a mobile phone is also a portable telephone connected wirelessly.
Let us consider a radio station. A tower broadcasts signals to a particular coverage area. When your radio is within this signal coverage area, you are able to receive signals from this tower and the signals are converted to audio form. You hear this audio as the songs and news. This is one way communication , where the signal is received from tower to the radio and the reverse does not happen. Now consider this coverage area as a cell and the radio as the mobile phone, the device is called as the cellphone. Here the communication is both way , sending and receiving the calls. This is to give you an idea of, what is a cell phone. Now there are many towers in your city, town or village. All these are interconnected wirelessly. When you travel at different places your mobile phone is in mobility under this tower cells and hence it is called a Mobile Phone or a Cell Phone.
Every mobile phone has a SIM card, given by the Mobile operator or carrier operator. The mobile operator can also be called as service provider. The mobile service provider assigns an unique identification number to this sim card, which is your mobile number. When you call a particular person mobile number, a connectivity is established from your mobile phone to mobile operator and later the call lands to the mobile phone operator of the other person and finally his /her mobile phone. Thus an end to end communication is established between the two mobile phones.
Mobile Phone is also called as a cell phone, Featured Phone, Smart Phone, Basic Phone, and handset.
Voice call is the main operation of a Mobile Phone. However there are also other services provided in the mobile phones in the modern days. They are short messaging service – SMS, games, chat, mail, browsing and other internet services. Smartphones have short range connectivity services called the Bluetooth and Wifi. Smart Phones have features like photography , apps, video games, messengers, social media, etc
Unlocked mobile phones are the one not attached to any service provider or carrier. You can choose any phone with the same phone number or sim card and also you can change the phone number or sim card of the same mobile. They operate under GSM network. However carrier phones or locked phones are the one attached to particular service provider or a carrier. You cannot change the phone number or mobile phone easily. Only after certain unlock process by the carrier operator, the phone can be unlocked from the assigned phone number. They operate under CDMA network.
Some of the carrier operators in United states are: