It is impossible to get speeds like that out of Sprint's 3G technology, EVDO Rev. A. It's maximum speed technically possible is 3MB. And no one really even gets that. Maximum real world conditions on the Sprint network are more like 1.5MB.
You either were connected to Wi-Fi, Airave or 4G and blissfully unaware. It could not be Sprint's 3G. Also, speedtest using Non-flash based tests are not reliable. On my Verizon BB I use for work, the speed tester I use will sometimes say I have 8MB to 20 MB. On a 3G Blackberry not on WiFi! Not possible. Use Speedtest.net or their app. Everything else is iffy.