Monthly Jpg Index Of/ What Is The 'effective Cost Per Month', On A Pay Monthly Phone Tariff?

What is the 'effective cost per month', on a pay monthly phone tariff? - monthly jpg index of/

I have never bought one, paid in monthly phone bill, but I decided to buy the new Sony Ericsson W705 out on his way out. I'll try to pay monthly prices and found a good deal! Except that I do not understand what the "actual cost per month: ..
Is this what we really pay? The agreement is perfect for me .. If I pay the "actual cost per month for 18 months after the offer ..
http://i205.photobucket.com/albums/bb190 ...
Can you help me and explain?
Is there anything I should know?
Thank you!