N8ter
Banned
There needs to be a balance between choice and focus. Too focused, and there aren't enough to choose from. Too many choices and things lose focus.
Personally, I think there should be somewhere between 2 and 4 devices per carrier.
Something I learned in sales a long time ago. Never offer a customer between one product, and the door. So currently, at least w/ Verizon & Sprint, (ideal world here, I understand what it's actually like in their stores) at best the customer is offered the choice between a WP and one from "the other guys". What you really want is to offer a choice between WP "A" and WP "B".
BTW - Next time you go buy some shoes, see if the sales person comes from the back room with one or two pair of shoes, even if it's the same thing in a half size different.
2-4 Sounds low.
Really, there should be more. There is no loss in focus as long as every device has its niche. For example one phone may have superior camera hardware to other devices, so it is worth it to stock it even when you have a ton of other phones running the same or similar hardware. The MT4G nad Amaze 4G on T-Mobile were good examples of that, as was the Vivid on AT&T and Rezound on Verizon Wireless. In from the same OEM, a device may be totally worth stocking because it offers something that may appeal to consumers that other phones do not.
If you go by general form factors:
Portrait QWERTY
Landscape QWERTY
Small-Mid Touch Screen (3.5-4")
Larger Touchscreen (4.3-4.8")
Phablet (5.3-5.5")
Tablet (7-10.1")
Gives you 6 opportunities to carry a device a different segment of consumers will want.
And that's not even taking into account devices that may be targetted at some types of prosumers (i.e. phones with ridiculously good cameras or PMP functionality).
There is nothing wrong with flooding the market. It means you will be able to appeal to more consumers than if you stick with only one form-factor. Not many companies can stick to one form factor and perform like Apple does with the iPhone. Most have to go whereever they can to get at those customers.