vmg3625-t50b Router Firmware

Hi,

i bought Zyxel vmg3625-t50b router from IPS and i wanted to change this IPS but they told me that i will not be able to use the router with another SP as its locked. Thus can i change the Firmware and use it with another SP. Is there any solution or i lost my money that i bought this router with.
If there are a firmware that i can use, which default login users and pass will i be able to use?

thanks