I own and use a SMT 5600 in daily life. The 5600 replaced an MPX-200, running the hacked 2003 ROM upgrade (what can I say, it didn't come with bluetooth). I have AT&T Wireless, which is now owned by Cingular (USA).

Last night, I decided to attempt to ebay the MPX200, so I swapped in my (blue) SIM from the 5600 and booted it up to make sure it was sellable. Oddly, the network that came up was "Cingular" without the "roaming" triangle. Unless I'm having signal issues with the 5600, it doesn't default to Cingular. In fact, on the 5600 I have to switch networks and use 310410, which is I believe Cingular's 850 mhz network code - and I always get the roaming icon.

Funny thing is, on the MPX200, under Settings > Phone > Network > Select A Network it *doesn't* list Cingular - only AT&T Wireless and T-Mobile. The 5600 always (seems to) list the network you are on as an option, in addition to other networks it finds.

Just to clear my head, I stuck the SIM back in the 5600 and fired it up. It chose "AT&T Wireless". I did check the registry of the MPX200 (HKEYLM > SOFTWARE > MICROSOFT > RIL > OPERATOR NAMES) and while there is no entry for Cingular, there are a few weird ones starting with 26201 and ending with 26204 (in sequential order). Apparently those *are* network numbers for T-Mobile, Vodaphone, E+, and O2.

Any ideas, folks? I'm stumped. The MPX200 is a US version, which is 1800/1900 only and never used to show Cingular before. I'm not aware of any Cingular 1900 networks in the D.C. area, and even if there were, it's not listed in the MPX200's "Select a Network" and the SMT5600 lists it as 310410.

.icedmocha.

This is what my mpx200 has been doing for a few months now, even though I'm still using my AT&T sim card. I'd say it's normal behavior.

How much for the mpx200?

It's on ebay at http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...item=5817421392
starting price $25, reserve $50.

It's in excellent condition, except it's missing the headphone jack cover. The headphone jack itself works just fine.