Thesis:
I strongly believe that mobile phones are necessary. My reasons for this belief are that these phones are convenient for business people who travel a lot, and they are handy for emergencies.
Argumentation:
To begin with, mobile phones are necessary in the case of emergencies. For instance, if you fall down a set of stairs in a building and are badly injured and can't reach a pay phone, it is handy to have one to use.
Or, if your car breaks down in the middle of the night in a strange neighborhood, it would be dangerous to leave it in search of a public phone booth.
My other main reason is that mobile phones are convenient for business people. For example, if you are out of the state or even overseas and you have to contact a client to do some important work, it is useful to have one to use.
By using a mobile phone, important information can be received. People can't stay in an office all day waiting for their phone to ring. Some people have to go and do jobs or they will go out of business. You can even send faxes or messages and use the internet with your mobile.