The most common case is when a girl asks a phone number - is the desire to become better acquainted with it. Make sure on what he wrote your number. If your hand, then you meet a guy sensual, romantic or macho, that shows you clearly that your dating him dearly. However, thus recorded phone can quickly wear out due to rain, for example. If he wrote the number on a piece of paper, it is likely he will soon lose it, and writes the number just in case. If your new acquaintance number scored in his cell phone, then wait for the next day call and extended communication.
Sometimes record telephone simply because you have valuable information for him. For example, your professional activity is closely intertwined with its interests. Indeed, why should lose sight of the familiar doctor, a lawyer, an interpreter, because they can always ask for help or advice.
If you innocently told her phone number unfamiliar person, do not be surprised when you will call strangers in order to sell you a product or service. Many savvy young people especially under the halo of its charm creep into the confidence of girls and lure their phone number, then to present them as potential clients, for example, in beauty salons. Likewise, you can invite the girl to the crowd on the film project, the casting or advertising campaigns that require your type of girl. It is quite possible that they are using a pickup appointment, after which the end of the day to count the number of collected phone numbers and find out who this time of the guys were on top!
If he wrote your number, write it yourself and phone number. So you'll know if anything, to whom to make a complaint.