[HTC Incredible S] John Anderton:
There are a few threads here which provide radios to flash and information on how to flash them. I am writing this guide so people know what the different ways of flashing a radio are and what the repercussions of each method are.

Flashing methods

Method 1) Using fastboot (Recomended)

Step 1) Download the radio. If the radio is a zip file, open it and extract radio.img

Step 2) Connect your phone and enable debug mode

Step 3) Use adb to send your phone to boot loader with the command "adb reboot bootloader". Alternately, you can switch off our phone and turn it on with power+volume down pressed and get teh same result

Step 4) Once you are in fastboot mode in the boot loader aka hboot and your phone is connected to the PC via the cable, type the command "fastboot flash radio radio.img" making sure radio.img is in the same folder as fastboot & your command prompt session

Pros of this method:

mainver doesn't change

Avoids issues such as Security Warning - Stuck in bootloader

Method 2) Flash from HBoot with PG32IMG.zip

Step 1) Download the radio which is in a zip file

Step 2) Copy it to a SD card which is a gold card. If you don't have one, create a gold card first

Step 3) Switch off our phone and turn it on with power+volume down pressed. This will take you to HBoot and the file will be flashed after confirmation from you

Cons of this method:

mainver can change based on the mainver mentioned in android-info.txt

Requires a gold card

Pros of this method:

You can reduce your mainver when needed.

Why is this a pro and a con?

It's a con because if you don't know about this and increase your mainver before installing stock, you could get a bootloader Security warning leading to your phone not coming out of the boot loader. Don't worry, that post I linked to also has a fix but it's a pain for your.

It's a pro because if you want to go back to stock and the ROM you want has a lower mainver, being S-off allows you to run unsigned code and that allows you to reduce your mainver.

The choice is yours. You decide.

FAQs

1) Why do I need a radio update?

It is said that when you install a ROM, you should have a radio to match to give you good performance and not have a negative effect on reception/battery life etc. (this is something I've read on XDA threads).

2) What do I need to flash radios?

An android phone (of course :P) which is S-Off.

3) Does it matter (for radio installation) if I S-Offed using a XTC Clip/AlphaRevX/Revolutionary?

No. If you're S-Off already, you're good to go.

4) Where do I get my radios?

Threads such as these exist

5) I'm going to go back to stock. What should I check?

Check your phone's mainver. If the ROM's mainver is equal to or greater than your phone's mainver, you can install it

6) How do I check what my mainver is?

Connect your phone and type the command "fastboot getvar all"

7) How do I reduce my mainver?

If you want to downgrade your to a stock rom with lower main ver, you can use method 2 and edit the mainver in android-info.txt inside the zip file, put the txt back into the zip and then flash it on your phone. Your mainver will be lower and now you can install a stock ROM with any mainver.

I personally choose to keep my mainver at 2.00.000.0 allowing me to install any stock GB ROM I'd want to :)