I totally agree with Gidget's wise advice -- this is normal at this age, and some volunteering with those less fortunate could help.
To add to that: Take care that you don't announce to your son, "You need to volunteer so you can learn to appreciate what you have and not be so negative!" If he realizes that's your agenda, he's going to resist and will look on the volunteering negatively too. See if you can get a friend of his, or a couple of friends, to participate in the volunteering as well. Is it something his Boy Scout troop does -- provide service or volunteering? If not, can you prod the leader to do it? I would not just wait on Boy Scouts, though. Find some opportunities and let him choose. He should volunteer doing something he cares about, so he doesn't feel it's forced on him for his own good like it's moral broccoli.
Have you talked with his Boy Scout leader(s), teachers, baseball coach, or other adults he sees regularly (parents of his close friends, adults at church if you do church, his music teacher if he has lessons etc.) to see if they also hear this negativity? Sometimes kids this age can be just fine and positive with other adults in other settings, but come off as very negative and even whiny with parents.
If these other adults all say he's participating, he's generally positive, he takes responsibility well, he interacts healthily with other kids on their watch -- then try to ignore as much of his at-home negativity and whining as you can, because he's doing OK. But if he is perceived as the "negative Norman" overall in his activities, or avoids interaction or participation consistently, there is something larger going on. If that's the case, I'd get examples from those adults and consider whether he needs to see a counselor. But otherwise, this is pretty normal.
I know you feel you don't want to hear the negatives any more (I've been there!) but do let him get out some of his negative vents at the start, without your commenting or correcting him. He needs to know he can get out some of these thoughts and you'll listen. Then you can start redirecting him with questions. He may feel overwhelmed and mad at you for saying "List something positive right now!" but may do better if you ask some leading questions: "What did you make at the woodworking event today?" "Why was English class bad today?" "I know you were concerned about the history paper--how did it go today?" Elicit some details from him and let him talk. And sometimes just flat-out distract him with something positive: "Hey, there's a baseball team party next week--what do you want us to bring for food? You can choose!"
My daughter is 13 and can "go negative" at times, though overall she is positive; however, she does have a few friends who are a lot like your son, always finding the down side of everything and making a negative comment about whatever's being discussed.
Regarding the cell phone, that's separate to me. When it comes to wanting an object (as opposed to complaining about an event or activity), that's time for saying once, "Sorry, no iPhone's in the future, if you don't like the current phone you have you can always leave it at home" and then saying nothing else at all. Be deaf to "I want, I want" but listen to "I was mad" or "This was bad." Big difference, in my book.