Well done on owning your own home - what's cool about the latest mobile -when you have your name in bricks and motar!! I also think it's understandable to feel how you are as you've gone from being a bit carefree with the old cash to having to think about it a bit more - it takes a bit of getting used to. It's so hard to get on the property ladder in this day and age and you've done it by yourself, brilliant. Fast forward a few years and your mate is still at home with his parents - I can guarantee he'll be looking at you green with envy - meanwhile all the time you're climbing up the old property ladder. I would imagine a part of him is even a little jealous perhaps now - it would only be natural.
Although you may not have as much money to go out it doesn't mean you can't have a giggle. So you don't feel recluseful and resentful - why don't you have a point of one night a week having the lads over, get in a few beers, playstation it up....it'll soon go from ''my cool mobile phone''...to ''lets get round to sluggys''.
Also when the mobile phone guru gives it the old billy big, if it was me I'd just shrug and answer non plussed ''these things don't really bother me nowadays, not now I've got my place, I prefer to concentrate on that''...if you answer in that kind of fashion a few times then he probabaly will give up on saying it.
I'm a few years older than you and know that you roll on a few years and having the latest mobile (for example) will not be important. Your mates will also start getting themselves on the property ladder and will have that 'first year struggle' and you'll find you'll start to do things at each others houses more. Meanwhile, you'll be a little ahead of them and probabaly will be a bit more comfortable with money and they'll be thinking ''wish I bought back then''.
Alternatively if you have a spare room could you rent it to a mate?
Sorry I've rambled - well done