I'm trying to find out, purely out of curiosity, how the Nexus 4 supports band 8 UMTS (900MHz).

Looking at teardowns, I can't see an amp used for that band, unless it's one which isn't clearly marked. There are discrete amps for bands 5, 4 and 2, and a multi-mode/band amp, the ACPM–7251 which supports band 1+5. Also strange why they used another band 5 amp when the multimode already supports it. All of the other listed supported bands are accounted for.

I chip I can't find any info in, is located next to the multimode amp, a Murata SWV GFD49. Would it be possible to use one of the other amps? The multimode supports 900MHz GSM, but lists supported UMTS bands separately. Or, depending on tolerances, what about the band 5 amp (it would have an obvious use then), whose upstream frequency is ~50MHz lower than band 8? Seems unlikely, but I can't see anything else?

Sources:
http://www.slideshare.net/jjwu6266/i...google-nexus-4
http://www.anandtech.com/show/6440/g...xus-4-review/7
https://play.google.com/store/device...icrosite&hl=en
http://www.ifixit.com/Teardown/Nexus+4+Teardown/11781/3
http://www.secomtel.com/UpFiles/Atta...0252EN-v05.pdf