Misty coming to visit Ash and co. in Sinnoh is a common rumor and has been around since the start. May had already made an appearance though during the Wallace Cup as everyone knows which further fueled the rumor since if one old friend showed up that might mean another (namely Misty) is likely to appear as well. How true this is I don't know, but that's how rumors pretty much work. All in all, don't believe that deeply into a rumor, this rumor is more of a "hoping it will happen" rather then something that will happen (though don't get confused, it could happen).

As for Misty travelling with Ash again, I sadly don't think this is going to happen (though I wish it did) as Misty is now a Gym Leader and her older sisters pretty much gave Cascade Badges away when Misty wasn't there (and were about to when Misty left to see Ash after Hoenn during the beginning of the Battle Frontier). The same goes for Tracey, as he is now doing his dream job of being Professor Oak's assistant. However Brock is probably staying because his is one of the few running gags that are still around and without him Ash and the female companion will probably starve to death or get lost in the woods. Wish Brock got more development though, like have him have something to participate in, but unfortunately Brock is just a supporting character as movie posters hint with them not showing Brock or any of his Pokemon.

The only time Ash ever makes a call is whenever he needs some training advice and Pokemon is Professor Oak's area of expertise. In the beginning of Ash's journey (also known as Season 1), Ash called his mother more basicaly because he needed advice on how to actually live on his own and the occasional encouragement. However as Ash gained friends and gotten more experience throughout his joruney he doesn't need that much of his mother's advice or words of encouragement.