On a recent trip to India I purchased the Reliance Connect data plan and was given a Huawei EC325 USB modem with a Windows only install CD. Took me a few hours to figure out the setup with Mac OSX on a MacBook Pro and hence the blog.
Download the Mac OSX drivers from here. Under category "USB Modem Huawei USB" download the "Huawei EC325 Driver for McIntosh (both Power PC and Intel X86 Processor". Unzip the downloaded file and install the corresponding pkg file.
After the install (You may need to restart your Mac) go to "System Preferences" -> Network and you should now see the "Huawei Mobile" on the left pane. See below screenshot for configuring the setting (note: These settings are only valid for Reliance NetConnect).
Download Thai version of configuring the modem from here