It is possible to send free SMS from some mobiles with some mobile operators. To achieve this you need to enter a special code that will bypass the billing-system of mobile operators. This code was actually meant for diagonistics and reporting purpose for mobile operators.
The code is *#746025625# (please note the * and # in front and the # at the end)
This code actually just stops the SIM clock on most Nokia and Sony Ericsson phones though some firmware versions on phones are unaffected. The clock stops for just about 3 mins and if your operator bills according to SIM clock time then you can theoretically make free calls. However, most operators now bill remotely according to their own clocks. Some operators may still allow free calls in their pre-paid schemes.
As for sms, many operators have a few message centers that allow free text messages to go through if they're sent immediately after entering this code.
Most operators though know about this code so its unlikely that you will be able to use this feature indefinitely - use it as a one-time emergency option.
