That happened to me ALL THE TIME with my Bionic.For three months I kept track of how many times a day it would happen, where it happened, what I had to do to get data back.
Like you said, airplane mode would fix it sometimes. Mine got to the point where a reboot wouldn't help.
Called VZW numerous times. Went through 2 sim cards and 4 phones. Last tech rep I spoke with said, oh yeah this is a known issue with this phone. I was like WTF, then why have I been dealing with this for 3 months?! Every other tech wanted to blame where I lived. That didn't make sense because it happened everywhere I went.
I'll stop ranting now because I could go on. I would suggest keeping track of it and keep complaining if it is an issue.
One more rant item....I've been with VZW for over 10 years and the replacement phones they wanted to offer me were no where near the tech specs of the Bionic which irritated me to no end. I understand my phone is a glorified radio device that may not have reception everywhere, so I don't sweat the little stuff. But my issue was happening all the time, everywhere I was.
Good Luck!