If O2's tariff has convinced you to invest in Apple's iPhone 4, be aware that getting one isn't just going to be a matter of walking through the door later this week.June 24th, or this coming Thursday is the first day of sales, but O2 has now admitted that stock levels will be low that day and in the early days of the iPhone's launch. That has prompted O2 into a 'priority' selling policy, which will give existing customers the first chance of buying Apple's latest smartphone.But don't despair, the 'one of us' area is spread fairly wide, including iPhone customers, general O2 customers, mobile or home broadband users and users of the company's recent home broadband service. Just as long as you've been a customer since 24th May 2010, you'll be fine.Or you could try one of the other networks. O2 is the only one currently with a selling policy like this, with others either quiet on the subject or stating clearly, like Vodafone for example, that everyone will be treated equally. Or in other words, the early bird catches the Apple-shaped worm on Thursday.