[brauntex]

Will there be any issues with using a non ATT 640 dual sim LTE version on ATT? Both sims are ATT, one personal & one business.
I know only one line is active at a time on calls or text, but how is data traffic processed in a dual sim phone?

[xandros9]

don't know how data is handled, but as long as the phone has all, or at least some of the cellular bands it needs to function on 3G, 4G... it'll work fine.

[Corepc]

From what I read here data is controlled via One sim only which you can choose, and calls & txt can be set by sims has needed.Cellular and SIM settings on Windows Phone | Windows Phone How-to (United States)

[brauntex]

Thank you both for your replies. Corepc, the link is excellent and I've bookmarked it.
I noted the announcement of the Yezz Billy 5 a while ago as the first dual sim LTE phone, but have not heard anything since.
One of these 640 models will undoubtedly satisfy my need very well. Can't wait for the launch to get rid of carrying 2 handsets.

[brauntex]

Here are the bands listed on Pdadb.net specification page for Lumia 640 Dual Sim LTE build RM-1077

Cellular Networks: GSM850, GSM900, GSM1800, GSM1900, UMTS850 (B5), UMTS900 (B8), UMTS2100 (B1), LTE2100 (B1), LTE1800 (B3), LTE2600 (B7), LTE900 (B8), LTE800 (B20)

These bands don't appear compatible with the ATT network in the US based on my limited understanding. Is that correct?

[Davide Carozza]

I may be misunderstanding (I don't know a whole lot about frequencies), but check out this link instead:

microsoft.com/en/mobile/phone/lumia640-lte-dual-sim/specifications/

Has way more listed than Pdadb, right?

[brauntex]

From the ATT U.S. support page on BYO devices:

You can bring your own phone or tablet to AT&T with no annual service contract, if your device is unlocked - not programmed to work exclusively on another wireless network, and will work on one of these GSM network frequencies:
3G UMTS network in the 850/1900MHz bands
4G LTE network AWS/700/850/1900MHz bands

From the Microsoft site referenced immediately above (microsoft.com/en/mobile/phone/lumia640-lte-dual-sim/specifications/)

Cellular connectivity
GSM network: 850 MHz, 900 MHz, 1800 MHz, 1900 MHz
GSM max data speed DL: EGPRS 296.0 kbps
GSM max data speed UL: EGPRS 236.8 kbps
WCDMA network: Band 1 (2100 MHz), Band 2 (1900 MHz), Band 4 (1700/2100 MHz), Band 5 (850 MHz), Band 8 (900 MHz)
WCDMA max data speed DL: 42.2 Mbps (Cat 24)
WCDMA max data speed UL: 5.76 Mbps (Cat 6)
LTE FDD network: Band 1 (2100 MHz), Band 17 (700MHz), Band 2 (1900 MHz), Band 20 (800MHz), Band 3 (1800 MHz), Band 4 (1700/2100 MHz), Band 5 (850MHz), Band 7 (2600 MHz), Band 8 (900MHz), Band 28 (700 MHz), Band 12 (700 MHz)
TD-LTE network: Band 38 (2570-2620 MHz), Band 40 (2300-2400 MHz)
LTE max data speed DL: 150 Mbps (Cat 4)
LTE max data speed UL: 50 Mbps (Cat 4)

I'm not very knowledgeable about frequencies either, but it appears the 640 LTE as listed on the referenced site should be compatible on ATT in the U.S.