Symphogear G will begin airing on July 4th. If you're in Japan it will air on MBS and TV Aichi (Thursdays), BS 11 (Fridays) and Tokyo MX (Saturdays).
Here is a release schedule for upcoming merchandise:
Symphogear Manga volume 3 - July 10th
Symphogear G Character Song CD 1 (Unknown character) - July 17th
Symphogear G Character Song CD 2 (Tachibana Hibiki) - July 24th
Symphogear G Opening theme single (Nana Mizuki) - July 31st
Symphogear G Character Song CD 3 (Unknown character) - August 7th
The information about the opening theme is unconfirmed at the moment, so it might change at a later date but the rest of this information is accurate. Current speculation among fans is that character song CDs 1 and 3 might feature new characters since Hibiki is the only character they've announced otherwise. However, the Amazon.jp listing for the 1st character CD states it will feature a "duet" meaning it might have more than one character on it (like season 1 with Zwei Wing).
The first CD is available for pre-order on CD Japan if you're interested in importing it.
There will be an early premiere screening of episode 1 on June 24th. There is a special lottery that you can enter on the official website, 1000 randomly selected people will be invited to the event which tentatively includes appearances by the 3 main actors, Aoi Yuuki (Hibiki), Nana Mizuki (Tsubasa) and Takagaki Ayahi (Chris).
New character design images from the official site:
New story details:
Season 2 will take place 3 months after the end of season 1.
Japan has joined with America and begun doing collaborative research on the Symphogear system.
A new complete relic (code-named: Sacrist S) was transported to an American military base.
A new enemy is lurking behind the shadows.
A large flood of Noise has spread from the treasury of Babylonia that Fine left open in season 1.
Hibiki, Tsubasa and Chris are charged with defending against the Noise onslaught.
And that's everything for today, but the closer we get to the premiere date, the more details we should get! Look forward to lots of new information trickling in during the month of June! I'll do my best to keep on top of it.