Tri-band Without 900 Useless?

[Effendi]

Yes, what I mean is that "traditionally-900" operators often give priority to 900 channels (they have more), while "traditionally-1800" operators will give that priority to 1800 channels. So I suppose that a 1800-only phone could have some problems with the first ones, while a 900-only phone will have with the latter ones.

In any case, a dual-band 900/1800 in Europe is almost always advisable.