Since the ICMP protocol belongs to the IP stack, it differs in purpose from protocols like TCP and UDP. Each ICMP packet is encapsulated in a single IP datagram, and so like UDP, ICMP is unreliable. By flooding 100 packets to your IP address, ICMP can measure the quality (not throughput) of a connection between two endpoints fairly accurately. For this test, an algorithm was created to determine the grade of a connection. The grade is weighted by three factors: latency, packet loss, and jitter. This test should be considered accurate only from endpoints located within North America (at least until I setup geographically diverse locations).
What are some disadvantages of this test? When initiating ICMP requests from behind a firewall, upon acknowledgement from the destination, NAT allows packets to traverse the firewall back to the source. Since this test originates from the outside (in relation to you) and not the inside, a firewall may be configured to deny & drop such requests, preventing packets from ever returning to the host of origination (your mobile device). In other words, until I build an iPhone app from where the connection originates, this is how it's gonna work.
This shouldn't be a problem for most 3G wireless users, but those connecting via Wifi will most likely encounter inaccuracies.