it is possible to call someone without letting him know your no. his phone will display "no number " or "restricted number".for some service provider it is enabled by default.u have to use your phone feature or find out the special code which you can prefix and call that no. for some other service providers like reliance it is not enabled by default,u have to call customercare to activate this feature .for rim this code is *314.u can prefix this code before any no. and call that no. hiding your own no. it works only after this facility is activated.