I've recently noticed poor 3G network speeds when using my iPhone, and wanted to conduct some tests to identify which of the following could be the potential culprit:

 1. Could it be the new 3.0 version of the iPhone operating system?

 2. Could it be the new 3GS model of the iPhone?

 3. Could it be a problem with my 3G provider, Vodafone España?

 SETUP

 I've run these tests using a MacBook with OS X 10.6, and both iPhone 3G and 3GS models, running OS 3.0.

 TESTS & RESULTS

 => MacBook tethering to 3G-connected iPhone (Speedtest.net)

 For these tests, I had the MacBook tethered to the iPhone, and ran the tests at Speedtest.net using the Spanish "Elda" servers.

 - MacBook tethered to iPhone 3G, 0.18 Mbps
- Macbook tethered to iPhone 3GS, 0.14 Mbps

 For comparison, here are the results when: (a) untethered, and connected to the local Wifi, and (b) tethered to the 3G-network via a different phone than an iPhone.

 - MacBook on local Wifi, 6.00 Mbps
- MacBook tethered to HTC phone, 2.5 Mbps.

 => iNetwork iPhone App Test

 For these tests, I ran the iNetwork Speed Test application on the iPhones, comparing the results of being connected to the local Wifi, and connected via the 3G network.

 - iPhone 3G: Wifi (2.3 Mbps), Vodafone 3G (0.12 Mbps)
- iPhone 3GS: Wifi (1.2 Mbps), Vodafone 3G (0.12 Mbps)

 CONCLUSIONS

 Based on the following tests, I conclude that the problem must be with the 3.0 version of the iPhone operating system.

 - It's not a problem with the 3GS model of the iPhone, because the performance was similar on the iPhone 3G model.

 - It doesn't seem to be a problem with Vodafone, as tethered performance using an HTC phone was fine.