For AMD cards Sapphire makes really good cards, and from what I know the voltage should not be locked. When using overclocking utilities such as MSI Afterburner or Sapphire Trixx you should be able to adjust the voltage on most cards. From what I have read some of the cards (Sapphire Vapor X) come with a voltage locked at 1.25v.
From what I read only a fraction of people have a locked voltage, but if you don't want to risk having a locked voltage, you could go with another brand. Check out some of the Asus DirectCu (do note that some of the asus cards used to have issues where the heatsink wasn't properly mounted causing overheating), Gigabyte Windforce, or a MSI cards. However it is strange that some people are getting voltage locked cards, apparently some cards from various manufactures are arriving voltage locked. Some people say that they set a fixed voltage to get around this though.
I found a thread on another forum about people having the same issues:http://www.overclock.net/t/1303929/7950-vapor-x-voltage-locked
Hope this helps!