In fact, Skype, just as a for instance, is worse on hotel wifi as launching the app on a laptop makes you a middle node for some conversations.
Per the Skype IT administrator guide, a Skype node will not become a supernode unless it has a public IP address and meets the memory, bandwidth, and uptime requirements. It will not become a relay node unless it has a public IP address and is directly reachable from the Internet.
It is very unlikely that launching the Skype app on a laptop on hotel wi-fi would meet these requirements.
In the last 5 seconds, without touching Skype or having any active voice or chat sessions open, my computer has had communication with 14 IP addresses. Here is a sample of some:
TiggerAir-i7-2:~ patrick$ host 220.127.116.11
18.104.22.168.in-addr.arpa domain name pointer 94-193-99-152.zone7.bethere.co.uk.
TiggerAir-i7-2:~ patrick$ host 22.214.171.124
Host 244.137.90.78.in-addr.arpa. not found: 3(NXDOMAIN)
TiggerAir-i7-2:~ patrick$ host 126.96.36.199
188.8.131.52.in-addr.arpa domain name pointer KD175129063150.ppp-bb.dion.ne.jp.
TiggerAir-i7-2:~ patrick$ host 184.108.40.206
Host 244.29.190.218.in-addr.arpa. not found: 3(NXDOMAIN)
TiggerAir-i7-2:~ patrick$ host 220.127.116.11
18.104.22.168.in-addr.arpa domain name pointer ETC-NALZAYER.ETC.CMU.EDU.
TiggerAir-i7-2:~ patrick$ host 22.214.171.124
Host 126.96.36.199.in-addr.arpa. not found: 3(NXDOMAIN)
Those do not look like Skype servers. I guess it is possible everyone in my contact list is somehow pinging me, but that seems a little bit silly.
My IP address is 172.30.19.19, hopefully I do not have to explain that this is not a "public IP address". I have been online a few minutes, so unless their uptime requirements are about the same as a regular phone call, it is too short. I will admit, I have plenty of bandwidth available, though.
In short, while they can claim my laptop is not being used as a supernode or relay, Skype is still randomly talking to a slew of IP addresses. Anyone know what Skype is doing?
Does Skype on $HANDHELD have the same property?
Not as far as I know, for the obvious reason that handheld devices have network connections that are suboptimal for this.
The above happens to my laptop when I am on 3G / EDGE, even when I have a 10-net address. In fact, one of the first things I do on 3G is kill Skype because it noticeably increases my network performance.
I haven't checked on my iPhone 'cause I don't have things like tcpdump & little snitch.