The reason many network providers SIM lock their phones is that they offer phones at a discount to customers in exchange for a contract to pay for the use of the network for a specified time period, usually between one and three years.
This business model allows the company to recoup the cost of the phone over the life of the contract. If the phones were not locked, users might sign a contract with one company, get the discounted phone, then stop paying the monthly bill (thus breaking the contract) and start using the phone on another network or even sell the phone for a profit. SIM locking makes it more difficult to do this.
No sim card is required to perform an unlock.
No you do not.
NO. You do it all from the comfort of your home. The whole service is remote, once your IMEI is marked as unlocked by ourselves the unlock is pushed over the air from Apple's servers to your device over either Wifi or your current cellular provider.
You tell us your IMEI, what network your iPhone is locked to, and what model iPhone you have. Having made payment, we then mark your IMEI as unlocked within Apple's IMEI database - once this is done we send you an email confirming this. The unlock is pushed automatically over the air from Apple servers to your device over either wifi or your current cellular provider. No stress, no hassle, no drama. Your unlock is guaranteed and is also permanent, meaning you can safely update your handset and sync with iTunes without ever worrying about it re-locking.
In the United Kingdom, mobile phone network providers are not obligated to provide unlocking, even after the end of the contract.
Ofcom, UK's telecom regulator, allowed 3 UK to sell a mobile phone with the SIM card permanently superglued to the phone!
In terms of legality of our service, the full Oftel 2002 SIM-lock position paper specifies that there is no SIM locking law in the UK; the regulator wants only "consumer awareness" - which means it is totally legal to unlock your iPhone.