With its massive screen and impressive specs, it's easy to forget that Optimus G makes calls too. On AT&T's network in the San Francisco Bay area, we never had trouble getting a signal or maintaining a connection. No dropped calls or other such problems.
As for the microphone on the LG Optimus, it's average at best, and honestly leaves a little something to be desired. Calls often had a bit of static in the background, and voices over the line were fuzzy. It was usually necessary to play with the volume levels in order to get things comfortable. We'd call it an average performance overall, not a deal breaker, but not a feather in the Optimus G's cap either.
Speakerphone performance was equally fuzzy. Calls needed to be kept at half volume to prevent voices from being distorted. The Optimus G has two pinhole microphones, and their range doesn't pick up well beyond sitting at the end of a desk. Within that range voices came in loud and clear.
Your contact information can be found the Contacts app, as is standard with Android 4.0: Ice Cream Sandwich. Unfortunately its been hijacked by AT&T Address Book, a rather quirky carrier app.
You can set AT&T Address Book up to back up to a server, which is great, because it makes migrating to a new phone a breeze, and it will preserve your information if your phone is lost or damaged. However, the app is a finicky beast and occasionally took over thirty seconds to open. We could never get a bead on when and why this delay would occur. These hiccups felt random, which is unacceptable, since it's the only way to get at your contacts information, even if you go at it sideways through the Phone app.
We've never been crazy about how ICS imports contacts information from social networks and then doesn't let you edit some of them. The Optimus G's People app is hampered by this, imposing inscrutable restrictions on which of your contacts can be collected in the Groups feature. It's a real shame, because it displays your friends using great-looking tiles. Luckily, favorites is far more functional and just as good looking.