Yes. You do still have to search either deck or discard for him though (which basically amounts to choosing whether to shuffle your deck or not.)
Just noting for those that would question why, this is an important thing to do properly. You
must search one of those places because of the wording on the card, and that has real gameplay implications.
First, it lets you either look at discard (which is normally disallowed) or look at and shuffle deck (which is normally disallowed), so it is important to remember to do one or the other when you play it on an Isaiah in play.
Second, you must take to hand an Isaiah if one is in the location you search, as it is not a "may" ability (unless someone can point out a rule I didn't know about that says you don't have to find one). You still can't put him in play (because the card is protected from abilities that would cause duplicate unique characters), but the searching is not optional and the card would default to hand since it cannot be put in play.
So to conclude: If Call is played on an Isaiah in territory, the user must search either deck or discard, shuffling deck if that is what was chosen, and if Isaiah is found in the selected location it must be taken to hand.
Edited because my brother pointed out part of the above had been incorrect
