dear TS....
all u have to to is read....
and u find your answers there....

Maxis iphone IS unlock AND can be use with OTHER sim card. When the phone is call unlock, it means u can use it with other sim card without a problem.
about the JailBreak, the jailbreak violate ur warranty of iphones so u cant claim any warranty after that. DO it at your own risk...

now please, i know its your first time but i REALLY hope that u could read some or google the answers before u start to ask because this is a very common question. if u got your answer please close this thread.

thank you...