That being said, I work in an area that has spotty 3G coverage and my phone is constantly switching back and forth between H+ and E. Most times when it switches it shows G for a few seconds. I also had a BBerry for two years and it did the exact same thing so I'm assuming it's ok as long as it doesn't stay on G.
If you live in an area where Edge gives you better reception, in settings you can set it to Gsm only.
This will also give you longer battery life.
I've tried setting to gsm only and gsm auto, with both settings my phone still switches back and forth from edge to hspa.
Iphone and Blackberry both have the option to use 2g (edge) only in the network settings. The inspire's network settings menu has several options that are locked, leading me to believe that ATT has simply disabled this feature.