When purchasing a cellular/mobile phone, you are normally asked for a Social Security Number (SSN). If you do not have one and are not eligible for one, you will be asked to pay a security deposit. The amount of the deposit varies according to the provider. There are alternatives to avoid the SSN or deposit requirement. One is to buy a prepaid mobile phone, which is possible to do at local stores such as T-Mobile in Harvard Square. Another is to use Cellular LD to make international long distance phone calls from your mobile phone. Please check here for detailed information.