After some years of using a Nokia 6300 purchased through my carrier, Cincinnati Bell Wireless, I bought a completely unlocked Nokia 5800 from Dell.
I get good GSM 2G coverage around home, but where I work (50 miles away) I've had coverage issues. At my desk in the building, I usually have one or zero bars. But sometimes I see a 3.5G or 3G icon where my usual GSM tower icon lives. But when I attempt or use voice or data in that 3G mode, it fails.
Through some Internet searching, I came across some information posted by "mdo77" at HowardForums:
1) Cincinnati Bell's 3G frequencies are 1700/2100 MHz, which is actually the same at T-Mobile's. AT&T uses the 850/1900 freqencies. All three companies (CBW, ATT, TMO) have the same 2G (EDGE) voice/data frequencies, however.
2) Any CBW phone that has any chance of 3G working has the 1700/2100 bands.
3) CBW's 3G footprint is local only. They have no 3G roaming agreements (at least any that are active). If you're outside of the Cincy/Dayton area, you're EDGE only.
4) Even if/when roaming in 3G is available for CBW customers, it will only be on the 1700/2100 (TMO) bands.
I suspect what's happening is that my phone is picking up the AT&T 3G signal and favoring it over any standard 2G GSM signal (there's actually an AT&T wireless building nearby). However, AT&T doesn't let me through because I’m not an AT&T subscriber. I suspect if I tried a SIM card from an AT&T Wireless friend, I would get AT&T 3G right my desk.
According to Nokia's specifications (http://www.nokiausa.com/find-products/phones/nokia-5800-Xpressmusic/specifications), the Nokia 5800 operates at 850/1900. It would seem, then, that the Nokia 5800 would achieve 3G on AT&T Wireless but not on Cincinnati Bell Wireless.
What troubles me, though, is that Cincinnati Bell Wireless sells the Nokia 5800. If the above is all true then why is Cincinnati Bell Wireless selling a 3G phone that won't work on their own 3G network? Is there any hope of the Nokia 5800 ever working at 3G speeds on your network?
Meanwhile, I've now taken my phone out of Dual Mode so that it still restrict itself to the GSM 2G network.