Mobile Phone Networks etc (Istanbul)

Hello!

İ have just arrived in İstanbul and am in desperate need of a mobile phone on a network here. İ understand that the pay as you go system is here, could anyone advise me of the best network to go with? İ am on a limited budget, do not need anything fancy just to call and text. İ also do not speak any Turkish which is problematic so if anyone knows a good shop where they speak English that would be great.

Thanks!

Amy