here are some iphone access codes to various funtions. With these you can check various Call status and options, whether they are Enabled or Disabled.
if you are using pre paid then you can also check if your account balance as well as quota post paid minutes, if applicable.
dial these numbers and then press call.
* # 43# ----it shows if call waiting is activated.
* # 61 #----- it shows if Call is forwared if there is no answer
* # 67 # ----- shows if call forwarding when your number is busy (on/of)
* # 33 and # ---- shows if outgoing call barring is activated or not.....