One of my current research & consulting themes is around what I call 'multiplicity' - the notion that future mobile users will have multiple devices and/or numbers, service providers, messaging inboxes, broadband connections, bills, social networks and so on.
I still regularly see presentation slides titled "The Power of One" or something similar - dispensing the 'obvious' wisdom that the future involves one device, one number and so forth.
This is marketing wishful-thinking that flies in the face of human nature, Moore's Law, competition & differentiation and assorted other factors. For every two things that converge, another three will diverge. If phones are both cheap & highly differentiated, why would you just want one? It doesn't mean you have to carry all of them, all the time.
Same with operator services - if they're commoditised, then sure, one is enough. But the paradox of competition is that if there is real differentiation in coverage, pricing plans, available devices, content/application partnerships.... then it's not surprising that customers will be promiscuous and want multiple suppliers, dividing their spending between them.
Sure, some people will be both loyal and adamant they want such a degree of simplicity that they'll happily confine themselves to a single 'thing'. But others - especially today's multitasking/multichannel youth - don't have a problem with managing complexity. If you're already happily juggling multiple groups of friends on MSN, Yahoo, ICQ, Facebook, MySpace & Bebo... adding another phone number ain't exactly difficult.
Some great evidence of this trend comes from this survey, apparently conducted by ICM for bank HSBC (I have no idea why & can't find the original press release). 45m adults, 70m SIMs, 71m phones - and 9% have 4 or more devices. My only question is whether the data assumes that only 'adults' have phones - I see plenty of 10-year olds with handsets, which might skew the analysis.
This correlates somewhat with other estimates I'd seen before, but if accurate seems to indicate an acceleration - previous estimates seemed to be in the range 1.2 - 1.4 per person, if memory serves me right.
The continued evolution of multiplicity is inevitable, in my view. Vendors and operators should take their heads out of the sand. As well as selling convergence products & services (which will certainly continue), they should also look to exploit and support divergence in parallel. Multi-SIM, Multi-Handset, Multi-Number services - and maybe even work with their peers to do cross-operator phonebook syncs and other services.
People evidently want lots of phones, numbers, operators, email addresses, whatever.... so make it easier, not harder.