That's the old RAZR gimmick.
And honestly it still works. Practically the entire line of HTC, Samsung and Motorola is still based on this principle. Samsung's most successful smartphone model in its entire history by far, the Galaxy S, is a testimony to this principle. HTC? Take the Nexus One, turn it into the HTC Desire, Droid Incredible, and even WP7 phones like the Mozart, Surround and Trophy.
Of course, the negative side of this is it creates support or update fragmentation, like what happened to the Galaxy S where i9000s got updated first and US phones last.
The bright side on the other hand, is that it keeps new models in front. Phones have a product cycle and its always in the launch "honeymoon" phase where it sells the best. Gradually, sales of the model in one particular area starts heading down after the first month. In a way, phone sales are like movie ticket sales --- always best in the first week. Its a rare blockbuster when a phone can hold its rank week after week after week. Globally, for a phone to sustain its sales, it has to spread horizontally --- as in launch in new markets, as sales tend to head down on existing ones.
When a phone is being marketed horizontally, that's when you see it being repackaged and renamed for different carriers. Example HTC Desire HD (GSM international) -> HTC Thunderbolt (Verizon) and HTC Inspire (AT&T). Galaxy S -> Vibrant, Captivate, Fascinate, Mesmerize, Continuum. Even the Nexus S.
We also see vertical marketing (business, youth, low end, high end). The Droid 2 becomes the Cliq 2. Vertical marketing however, is limited by affordability, since you can't move high end phones into low end youth segment because you lose money. It happens with Nokia only because these high end architectures have aged long enough and has become very cheap by volume amortization, and newer high end architectures take the place of the old ones. With Blackberry, expect newer Curves to take on Bold specs while the newer Bolds go into a new generation of more powerful designs.
In any case, we must note that Nokia is also losing because it doesn't that much control of its supply chain like Samsung does. Everyone has lost potential sales the last six months or so because phones are delayed and they are delayed because there are not enough parts to make them. Except for Samsung because they manufacture every part of the chain from the CPU to the screens to the NAND, which are the three most critical parts holding up the phone. Ergo, Samsung overtakes even the much vaunted HTC as a smartphone maker, leaping over Motorola at the same time.
The screen supplies are the most particularly serious. The bigger they come, the harder they are to get. Especially if they are AMOLED. It was logistically, a big mistake on the part of Nokia to pick AMOLED as the basis for its X7 and E7 screens because it literally handed over their fate to Samsung.