Why don't we trade them in, like we do our cars? Is it an inability to let go of a gadget we've spent so much time with and formed a special relationship with? Is it a back-up - just in case the new one dies? Is it that we can't be bothered going to the trouble of bagging it up and sending it to one of those 'sell your old mobile for cash' addresses?

According to David Edmondson, CEO of eRecyclingCorps, the trade-in is just something the industry hasn't got around to nailing properly, although I suspect mobile telcos may have been reluctant because they calculate the longer the user uses a subsidised phone, the better. Why highlight the trade-in option when any usage beyond the contract period is almost pure profit?

Why indeed? Well, Edmondson has the answers. His company offers a 'comprehensive' trade-in service - the user is given the trade-in price on purchase; then, at the end of the contract, just goes into the shop, hands in his/her phone and the figure is deducted from the cost of the next phone, or is credited to the account. No more dead phones cluttering up the Man Drawer. (see -You go into the phone shop with one and leave with two. Why?)

It's an interesting business model and a compelling case and there were many such at Mobile World Congress. This article highlights three of the business model video interviews we conducted there.

Rapid change always creates the best niche markets. iBwave, for instance, specialises in software to help the operator improve the signal inside buildings. Essentially the product simulates a building interior from a radio propogation point of view; then it evaluates the different electronic solutions on cost and effectiveness. (see - Tackling the indoor signal problem)

"When we started 'in-building' wasn't even a word, says Mario Bouchard, CEO of iBwave, "but now 80 per cent of the traffic is indoors while most of the network is outdoors." iBwave claims first mover advantage in what is clearly a fast-growing niche market.

Alistair Hill, co-founder of On Device Research, for instance, (see - Mobile surveys online) is offering a new take on the permanent consumer panel idea. Everything (opinion formulation opinion gathering and so on) is conducted with the least possible friction by being online and going through the mobile itself (or via the Web). Very large panels of users are formed and incentivised, companies who want to know specific things are able to come online and ask questions of them. It's Survey Monkey with the responders provided.VIDEO:You go into the phone shop with one and leave with two. Why?

David Edmondson, CEO of eRecyclingCorps, explains why the mobile 'trade-in' will soon be the norm - as common-place as trading in your car. Trade-ins, he says, can be a source of value for the telco, a source of joy for the user (98 per cent of consumers want to trade in their phone at purchase if they're offered fair value) and a lifeline to the hundreds of millions who aren't yet connected but who CAN afford a second-hand refurbished phone.VIDEO:Tackling the indoor signal problem

iBwave has built a very solid business selling telcos indoor radio signal optimisation software as their customers demand that tablets and phones work just as well in-building as they do outside. CEO Mario Bouchard tells Ian Scales how the product simulates a building interior from a radio propogation point of view and then evaluates the different electronic solutions on cost and effectiveness. VIDEO:Mobile surveys online

Finding new business models in new patterns of mobile behaviour is what this business is all about. Alistair Hill, co-founder of On Device Research, talks to Ian Scales about how his company has come up with a way to gauge mobile user opinion in growth and emerging markets.