Unlocked iPhone 4 from UK not working with India SIM

Your sim could be faulty. Try and get a replacement sim from vodafone, and see if that makes any difference. You said your phone is unlocked and you've used another carriers sim with your phone, so I dont see any reason why your vodafone sim would not work, thus I believe the sim is faulty.

Hope I helped. 🙂

Donnie.

Well I'm not sure anymore. If I was you, I would take my phone to an apple store, or an authorized repair shop. I do not understand why your phone cannot use vodafone sim card, when it can obviously work on any other sim. So take your phone to an apple store and have them take a look at it . Hope I helped. 🙂

Was the phone purchased from Car Phone Warehouse? If so, they are not truly unlocked and will lock to the carrier of the first SIM card installed.

How was the phone unlocked?

Who was it locked to prior to unlocking and using with Vodafone?

Did they authorize the unlock?

Al Iyer wrote:

It might have been I can't remember. But the contract was originally with O2 and I unlocked the phone

How, EXACTLY, did you unlock it? ONLY the carrier it was locked to can authorize unlocking it, which is completed by restoring the phone using iTunes. If you did anything else, you hacked it and rendered it unsupportable.

Having used it with another carrier is not evidence that it was legitimately unlocked.

Just to be clear, is this what you did? http://support.apple.com/kb/ht5014

Or did you walk into a carrier shop and walk out with an "unlocked" phone?

Try a SIM from a supported carrier in India. http://support.apple.com/kb/ht1937