Is there any way to use UPnP for NAT traversal on Android with a 3G/4G connection, and if so, is it carrier dependent?
No, for the time being thee is no way to do that, for the simple reason that the mobile carriers don't use residential-class NATs - what they have is "Carrier-Grade NATs" CGN, see here http://en.wikipedia.org/wiki/Carrier-grade_NAT, and these devices have very different port allocation and management mechanisms from the residential gateways.
See the Carrier-Grade NAT (CGN) related documents in this collection: http://www.scribd.com/collections/3292450/P2P
PS there currently is a UPnP-like protocol that is contemplated for CGNs, namely the "Port Control Protocol" (PCP), see here: https://datatracker.ietf.org/doc/html/draft-ietf-pcp-base-29
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