To help avoid such headaches, you could use an EDGE only device, or one which permits configuring EDGE only as needed. There's more work on the latter option sometimes depending on the handset you use though. Also, where precisely you are using the phone/service plays a huge role in when you'll bounce between EDGE & 3G/UMTS.
I would definitely switch away from the LG VU for a better ATT network experience. Try any basic Nokia 3G handsets for a quick comparison of how voice calls can sound much better than what you have now.
I currently have an LG VU on AT&T network and travel a corridor with several cities. My phone it seems is constantly switching between the 2 networks causing call interferance/break up, and generally poor quality. Is there a touchscreen 3G phone with a smooth unnoticed transition between networks that will allow me to maintain clear clean voice calls with AT&T or am I to be limited to an EDGE only phone to avoid this annoyance?