nah only people thats within 30 ft i think can only chat and battle with you and after the elite four you are correct you need to go to the 4-7 islands after you get the ruby from Mt.Ember where those rocket grunts are defeat them go inside u should find slugmas go through all the boulders usin strength after all that get the ruby plate go to the stairs get out and return to cecelio(spelling) and he'll give you the tickets for the islands
The day has arrived where I put in my very own signature with Fiend Codes:
SSBB = 0259-0069-0106
Pokemon Diamond = 4596 9316 5087