Just on the phone front...I can understand what you are saying Ghosty about the respect thing, but I'm with sue on this one. I think that it is demeaning to a teenager, my sister is 17 and would be very upset if she were expected to ask. Yes the parents pay the bill, but they also buy the food, you wouldn't expect them to ask before getting something out of the fridge.
Oh course I don't think it would be unreasonable to set limits, as sue said, on the phone use.
Stuggling, the way you describe it, its not the mess in his room you have a problem with, but the visibility of it, is that right? Its a sad but true fact that teenagers simply don't have the same priorities. I think that it is totally reasonable to expect hom to tidy his room, but his standards are going to be radically different from yours and as such he may not get why you are bothered by this.
I would persevere with the tasks you are asking, but teenagers need alot of nagging. Try not to lose you temper but talk to him. Let him know that you feel this is reasonable, and if he doesn't agree you're going to have to find some middle ground.
My friend is a psychologist and told me that teenagers and toddlers actually have pretty similar psychological make up. They are both at a stage where they are trying to assert themselves as an identity separate from their parents (or step parents). Its a time of growing independence for both, of fustration and sometimes resenting the parent for actually still being needed as much as they are.
How old is your ss? You say that you think that your DH isn't as bothered because of the real parent relationship, but unless you are really having problems with being a step parent, it may be more that you are unsure of what to expect of a teenager as opposed to a young child. You'll probably end up tearing your hair out when you own little one reaches the dreaded teenage years.