How does one know the right time to sell on a phone?
as soon as the next budget king appears, get one on order and put your current phone up on ebay.
so basically your one of the first to sell it on.
you will need to be active on these forums as well as modaco for new budget phones appearing.
all the phones i purchased before for the wife were all £100 or cheaper. these phones don't tend to depreciate much if at all within a short space of time of say less than a year. so basically the next time a phone appears for £100 or less and has even a slightly better spec, sell your current phone and buy it.
it is also fun, constantly buying and selling phones, having a new toy to play with. in fact it's so enjoyable once you buy a high end phone and stop doing it, your looking to upgrade when you don't really need to and are going to lose out because high end phones cost a lot more so they do depreciate.
basically i would be looking to hold onto the y300 for 8 months maximum, theres always another "great" budget phone being released every 6-12 months or so.
ZTE, Huwaei and Orange re-brands as well as t-mobile re-brands are the ones to look out for usually.
like i say if you upgrade often and quickly enough, you don't lose any money and your basically getting free upgrades for life.
we both have nexus 4's now though, because they were the first "cheap" high end phones. waiting for the next nexus before upgrading and will need to ebay them as soon as we have the new nexus on order.