I bought a used iPhone 4. The previous owner re-set the phone, but did not remove the device from their iCloud. It is asking me for their iCloud information when I try to set-up the phone. I don't have contact with the previous owner anymore. Is there a way to remove the device from their iCloud so I can use a new one?
Officially Remove Activation Lock
There is a way to remove iCloud Activation Lock.
You will need to make an appointment at an Apple Store. Provide the Genius on hand proof of purchase (to show you're the authorized owner) and proof of identity and they will reset Activation Lock, giving you access to the device.
If you bought it second hand, then you will need the seller, in person, with you when you take it to Apple. The seller will need to show proof of purchase, etc. They will then transfer the device to your account or simply remove Activation Lock.
A Dead End
What you can't (and never will) do is bypass it yourself or through some online service advertising it can. The device's identifier is seared into Apple's servers. They will, effectively, chase that iPod or iPhone till the end of time. Someone may be able to bypass it once, but once Apple's servers see it pop up on their grid, it's going to get bricked again.
The very nature of Activation Lock is that it is impassible so that the device can still be tracked by the owner if it is lost/stolen. You can't bypass it — the only way to remove it is by deleting the device from Find my iPhone on iCloud.com or logging in using the Apple ID that was used to set up Find my iPhone.
You can read more about bypassing (or not) Activation Lock in the following question:
protected by Community♦ Mar 4 at 22:38
Thank you for your interest in this question.
Because it has attracted low-quality answers, posting an answer now requires 10 reputation on this site.
Would you like to answer one of these unanswered questions instead?