T-Mobile has some serious buffering issues. I've seen a 70-minute ping RTT before. http://sprunge.us/hdUd
You can easily cause multi-minute latencies by blocking the radio, then unblocking it after a few minutes - the replies all come flooding back in. You can also see this if you start a ping and then go do a few speed tests or some large downloads - you'll see the RTTs climb and climb as the transfer goes, then they come flooding back once it's done.