Int'l Frequencies for Blackberry Wireless Devices?

hargass asks: "My US-based company is entrenched in AT&T. Now, as we look to expand our Blackberry 'fleet' from 1 to 5 units, I am struggling to determine which model will best suit our needs. My options are: the Blackberry 7210, dual band (1900 and 900 MHz); and the Blackberry 7280, tri band(1900, 1800, and 850 MHz). My users travel internationally, from London to Sydney to Beirut, and so on. I've researched what frequencies are most used outside of the States, and it appears that the 900 band is the most prevalent. However, the 7280 tri-band model doesn't operate on the 900 frequency. Is the 900 MHz frequency on the way out? Are the 800/850 frequencies the wave of the future? What are the strongest bands in Europe? Internationally, how much will not having the 900 MHz frequency hurt?"