Because at the moment there is no software solution for decoding iPhone 4 (with iOS 5 baseband) and iPhone 4S terminals, the only solution for decoding remains the payment made to a GSM service or to a person who decodes terminals. On the iDevice.ro forum exist several such people, but one of them checks for free the network on which an iPhone terminal is coded. Normally, such an operation costs between 2-5€, but on the iDevice.ro forum you can do it for free within the time limit available to the respective person.
Go to this link, ask to be told the network on which the terminal is coded and if you are lucky you will find out in a short time without paying anything.
