Would like to unblock a phone number

To unblock a number that you have blocked by mistake on your phone, follow these steps:

1. Go to the phone's main menu and select "Contacts."
2. Scroll down and select "Blocked Numbers."
3. Select the number you want to unblock from the list.
4. Select "Remove" or "Unblock" (depending on your phone's model and software) to unblock the number.
5. The number is now unblocked, and you will be able to receive calls and messages from that number.

Have them call again, do not answer, click lower left of phone and it will ask "unblock" number, select that.

Its easy..

go into phone settings select call/text barring and follow promps to unblock

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PUKs, or personal unblocking keys, are used to unblock a mobile phone which becomes blocked. Mobile phones may become blocked when a PIN (personal identification number) is entered incorrectly on three consecutive occasions. In some instances, the phone may become blocked, which requires a PUK to unblock it, and in other instances, the SIM (Subscriber Identity Module) card itself becomes blocked and again will require a PUK to unblock it.Mobile phones are also blocked when they are reported stolen and if there is an outstanding payment on the account.It is important to differentiate between unblocking phones (using a PUK) and unlocking mobile phones (using another type of code). NOTE: It is a criminal offence for anyone to attempt to unblock a mobile phone, other than the network provider who put the block on the phone.If your phone has become blocked by mistake, for example you have entered the PIN incorrectly on three consecutive occasions, then you need to contact the mobile phone network operator with your details. To explain a little more, specific to your mobile phone network, You need to go to your Service providers, web site & navigate your way to the specific PUK details for your mobile phone network operator. Usually you have to Register your phone to get a PUK code.

first you need to look if it has an imei number. this is located usualy on a sticker under your phone battery. then ring the phone company the phone is from and let them know you have bought it second hand, they should un block it.
otherwise find a local phone shop or phone stall on a market they should beable to unblock it, it usually costs around £10

There are a few services that make it easy to find the real number of a blocked or restricted caller. They do cost money (some as low as $5.00 per month to unmask numbers) to use with your cellphone.
You can even get the name and address of a blocked caller. Check into caller id unblocking services. Hopefully that will help you out.
Unblock restricted numbers with Trapcall's Bug Trap

Usually to permanently unblock the number, you need to contact your phone service provider and ask them to unblock your number. You can then block it per call if wanted by dialing *67 before dialing the number.