re: the sodding iphone/house purchase fallacy that comes up every single time on these threads:
a) only a small minority will actually splash out on the latest iphone as soon as it's released. Most will wait until their contracts end and/or they can get a good deal
b) it's not £50 a month compared to £0 a month expenditure on phones. The vast majority of people, not just young people, have smart phones now, so, its £50 compared to, say, £30, so actually only £20 p/m saving
c) Paying even £50 for a top quality smartphone with all the features means you don't have to pay for those features separately as you did years ago, so you save the hundreds or thousands you would have spent on: (delete as applicable) books, sat nav, camera, ipod/cd/vinyl player, laptop, phone call costs (because you use skype etc instead), diary, voice recorder (for work), even a tv for people who use their phones for streaming. This is both convenient for younger people who, if they rent, have to move often, and usually don't have a huge amount of space for storage, and ultimately not uneconomical.
Secondly, as others have said £4000 (although actually as I pointed out it will be more like £3000 unless they go without a phone completely) isn't even the 5% deposit needed even on a cheap first timer property at £100,000 (of which there aren't any in some areas of the country) - before you even start thinking about solicitors fees, removal costs, insurance, etc.
Also, don't forget that a deposit isn't the only thing preventing younger people from buying a house - lots aren't on permanent contracts which mean even if you had a deposit banks might not lend to you, especially on a single salary.
Student loan repayments are also now considered for the affordability criteria when applying for a mortgage, so even if you're on a decent wage if you are paying £80 p/m in repayments you're less likely to get accepted than someone earning exactly the same wage as you with no loan.