i would like to know if it is possible to make a mobile phone call in thailand to a company or person without showing my number to the recipiant.i have called large companies before only to be bombarded after by unwanted promotions ,thanks guys

on pre paid AIS 1 to call you can.

http://www.ais.co.th/12call/en/private-number.html

On a smartphone or iphone you can change call settings to hide your number.

This is a network-based service rather than a device-based service. So the network must support the blocking of the CPID, if it doesn't, then your device cannot support it. As you can see, AIS/One-2-Call offers this as a fee-based service - either for the month or on a call-by-call basis. I searched the DTAC/Happy and TrueMove H websites quickly and did not see a similar offer.