Simple 3G emulation on OS/X. Remember to reset the IP Firewall after doing this by 'sudo ipfw flush''.

simulate_3g.sh

#!/bin/sh
#
# simulate_3g.sh - Simulate a sluggish 3G network with delays & packet loss
# Usage: simulate_3g.sh 8080 8081

# Make sure only root can run our script
if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root" 1>&2
   exit 1
fi

# Simulate http over 3G, 300kbit/s with 5% packet loss and 200ms delays
# into all ports given as a parameter
ipfw pipe 1 config delay 200 plr 0.1 bw 300kbit/s
for var in "$@"
do
    ipfw add 1 pipe 1 dst-port $var
done