USA visit for 15 days

[inquisitor]

Yes, AT&T's 3G network operates at 850 and 1900 MHz so the HTC One XL would be fine. As of the Desire's AT&T-compatibility it depends on which version you own as there are three:
900/2100 MHz [Model A8181]
850/1900 MHz [Model A8182]
850/2100 MHz [Model A8183]

If you got your Desire from Telstra it's probably the last-mentioned version, which could register on those AT&T cells that run at 850 MHz but not on those working at 1900 MHz, which are primarily used to add capacity in urban areas.
If it's from 3, Optus or Vodafone it's probably the first-mentioned, which doesn't support any American 3G frequency.

[alect]

Originally Posted by inquisitor

Yes, AT&T's 3G network operates at 850 and 1900 MHz so the HTC One XL would be fine. As of the Desire's AT&T-compatibility it depends on which version you own as there are three:
900/2100 MHz [Model A8181]
850/1900 MHz [Model A8182]
850/2100 MHz [Model A8183]

If you got your Desire from Telstra it's probably the last-mentioned version, which could register on those AT&T cells that run at 850 MHz but not on those working at 1900 MHz, which are primarily used to add capacity in urban areas.
If it's from 3, Optus or Vodafone it's probably the first-mentioned, which doesn't support any American 3G frequency.

I thought it was the 8181 but we did get it from Telstra so I guess you're right (and it has been used successfully in the US before which supports the 8183 assumption).

The desire is only a fallback if she can't get a micro-SIM for the HTC ONEXL. Hard now to pick up and use the Desire after having had the ONEXL for a few weeks ONEXL is damn fast!! and the screen beautiful!!