It would not be profitable for the carrier to combine both of these but it would be profitable to the phone manufacturer. I can imagine people buying these dual mode cellphones and switching between carriers whenever the carriers offer more competitive rates as they jostle each other for market share. Such a phone would be useful for people who travel and move around and do not like to be tied to anyone carrier regardless of where they are.
CDMA is not going away as shown in Apple's rumour of introducing a CDMA iPhone, and with India becoming the world's second largest CDMA market surpassing China. That's a heck of a lot of CDMA users that is NOT within North America. In North America, CDMA market share accounts for over 50%.
So, I can see a lot of business sense to introduce a CDMA iPhone, but I also see a lot more business sense to introduce a "worldphone" that can do all GSM+CDMA+HSPA modes. It might not make sense to the carriers but it makes sense to the people who buy these all-in-one phones as it allows us (users) to control which carriers we want to choose, and not the other way around.
Right now, if you are with Rogers, you don't want to switch to Telus, Bell or vice versa due to different phones required due to incompatible networks.
With prices coming so cheap for a GSM/HSPA or CDMA/HSPA phones, how much more expensive is it to bundle both phone technologies together and charge a higher premium for people who want to be able to choose their carriers? I've seen videocards with more powerful GPU cores than desktop PCs, and laptops with their PC prices going down every month, but yet cellphones can't do the same, come on! Get real.
I can't see it as that much higher cost-$$ wise than what people are paying now for a Nexus One etc. It just makes sense to me to support both technologies within the same phone (dual-SIM etc). The carriers would like you to think different as it makes more money for them.
But doing it the other way would make the cellphone manufacturer more money (not necessarily the carriers) but also allow users control of their carriers. This would indirectly force the carriers to be more competitive since they have no more head-lock on their customers, and also this competitive rate-wars would directly help users to offset the higher cost of such dual-mode phones for future.
Again, just a different line of thought. Think outside the box... back to more head-banging sessions...