I thought '04 - '06 3's could work with any flip key... and in '07 the 3's were changed... I might be wrong... most likely am.The key half of the flip remote is the same between every Mazda with a flip key.... just like the regular key will work in any Mazda. I don't think the remote from the Mz5 can be programmed to the 3's computer. There is a compatible remote from a Mx5 that doesn't have the extra button but it's about 3x as expensive.
Honestly I like having the extra button because it makes the panic button half the size and that way it doesn't get hit in my pocket nearly as much.
I thought '04 - '06 3's could work with any flip key... and in '07 the 3's were changed... I might be wrong... most likely am.