You have to beat the battle brains (6) which are like super hard gym leaders.
You can always battle there again whenever you want to.
You unlock Silver Prints by beating the Frontier Brains in the Battle Frontier in Platinum.
Beat the Pokemon league and then go to olivine city and go into the building that was previously under construction. You will then be escorted the the battle frontier
beat the frontier brains
You get a Symbol by beating one of the Frontier Brains, the bosses of the different facilities at the Battle Frontier. Once you win enough battles in a certain facility, the Frontier Brain there will challenge you. If you win the battle, you will get a Silver Symbol. Beat that Frontier Brain again and you get a Gold Symbol. You can get two Symbols (silver & gold) for each of the facilities in the Battle Frontier.
You can't beat the frontier. Mostly because they just see how long you can keep winning in each of the battle areas.
Beat Elite Four.
Battle 21 trainers without losing in a row and then you will face Palmer the frontier brain if you beat him you will get a silver print and if you beat him again you get a coloured print these are found on the vs recorder
beat the battle frontier, collect every gym leaders pokegear number and beat them at level 100. then your done. also get mewtwo in cerulean cave.
there is no battle frontier in Pokemon pearl,but there is a battle tower. you can go there after you beat the elite 4
The battle frontier has two kinds of symbols you can obtain. If you beat Palmer the first time around, you get a silver symbol. If you beat him the second time around-much harder- then you will get a gold symbol.
after you beat a certain amount of challenges you will battle a frontier brain which is sort of like the gym leader. if you beat them you get a symbol
After you beat the Elite Four, go to the Battle Frontier.