Tri-band Without 900 Useless?

[Przemolog]

Originally Posted by DRNewcomb

If you are planning for her to buy prepaid SIMs be sure that the carrier she picks supports GSM-1800-only operation.

Good point, DRN.
And it doesn't have to be only the matter of coverage.
Once I read that using a 1800-no-900 phone may encounter problems in 900/1800 networks, even when you're in 1800 service area. It's because some networks are configured to "force" the phone to use 900 first, and 1800 later, if 900 is busy. That's 1800 only phones may be useless despite there's 1800 coverage.
I don't know if it's true - I couldn't check it by myself because I've never had a 1800-only phone . Does anyone know more about the problem menstioned above?

And one more, general remark.
I don't understand what is the sense in producing 850/1800/1900 tribands? For American users 850/900/1900 would be more useful. And, I think that GSM phones nowadays should be produced as 900/1800, 850/1900 (for Uncle Sam and the neighbourhood ), or quad-bands 850/900/1800/1900....