Will my iphone lock to my sim card?

Hi, I bought the iphone 4 16GB second hand so it had already been used and had already had a sim in it and was locked to that but the seller managed to unlock and then sold it to me. I was wondering seeing as it has already been unlocked once when I put my Vodafone sim card into it will it lock to that carrier or remain unlocked allowing me to use another carrier such as Orange or T-Mobile?

If it was manually unlocked or hacked unlocked or jailbroken unlocked, then it will remain unlocked until your do an itunes restoral or factory reset… After the restoral or reset, you will need to re-unlock it for it to work with your sim card again.

If this is factory unlocked, then it will remain unlocked until the day you die.