I restored my iPhone but it always says Activation Error, what should I do? I forgot my passcode so I go on iTunes to restore it, but after the restoration, it says Activation Error after I put in the Wi-Fi Settings. I have tried it many times but it still hasn't worked. 

I didn't jailbreak my phone, just forgot the passcode so I restored it. I do not have any SIM card in the phone.

Is there something I can do to get the phone in working order again?

Is there any way that can avoid using SIM card?

**I fixed it ;)**
Activation through iTunes or Over the Air (OTA) is when the device checks to determine if it is factory or carrier unlocked or if it needs a SIM to be activated.

It's almost certain that your failure to activate is due to not having a SIM card from the proper carrier. You do not need to have an active contract or phone number associated with the SIM (I have a 3GS which has an old SIM without a plan), it just has to be for the correct carrier.