how to calculate a SIM unlock code

I learned two things today.
1. Persistence pays off
2. Locked Phone and SIM Lock are different things.

Background, I am an ATT customer being serviced my Cingular.
I do not wish to change my service plan.
Many Cingular reps lied to me telling me that I could only find an ATT phone or buy a Cingular plan.
I decided to roll the dice and purchased a new "Unlocked" GSM world phone from Ebay (Motorola MPX220).
I popped in my ATT SIM card and the new phone presented a message saying "SIM LOCKED".
I telephoned Cingular and was told that I would have to call Motorola because it was a locked phone.
I called Motorola and received a very detailed explanation about locked phone vs. locked SIM card and that my problem was with the SIM card not the phone.
I called Cingular back and heard the same song and dance about having a locked phone and there being nothing they could do. I suggested we conference call with Motorola and was then transferred to another service rep who identified my problem as a locked SIM card which has nothing to do with the phone.
The Cingular rep then asked me for the 20 digits printed on my SIM card and then provided me with 2 coded to enter. The first caused my SIM card to ask for a PUK code and once entered my phone worked properly.
Be persistent and explain that the problem is with their card not your phone. They can absolutly help you unlock you SIM card for FREE!!! Answered Dec, 21 2010

You don't need to calculate a SIM unlock code they will deliver the unlock code to you through mail.
visit the site Unlocking4u.com here they are providing unlock code for your Siemens SX56 at low cost and unlock it.After unlocking,you can use any GSM Network SIM card on your mobile. Answered Apr, 06

Airtel sim card blocked ? this happens when mistakenly typing a wrong pin code or by changing network connection in Manuel if sim card is blocked and asking for puk code don’t be panic and enter wrong puk code for about 10 times ur sim card will be rejected

just type your mobile number and sent to 785 (EX; 9894951236 to 785)
Shortly u will receive ur PUK code in ur mobile message inbox airtel sim blocked solution,
what to do whenairtel sim card is blocked by mistake, entering wrong pin number

The source:http://www.blogtrickz.com/unlock-airtel-sim-blocked-puk-code.html Answered Jun, 30 2011

You can use this soft 

Bonrix SMS Server 4 Huawei 3G/HSDPA 1.0

hope to help

Answered Aug, 10 2010

You can use this software

 http://www.mobilefiledownload.com/article/free+calculate+palm+centro+imei+unlock+code.html

Answered Oct, 21 2010