If you're reading this then I take it you have already seen the first episode of the Idolm@ster Cinderella Girls anime that aired today. And for a lot of people this is probably their very first exposure to anything Cinderella Girls related, so I thought I could at least point you in the right direction if you wish to know more about Cinderella Girls.
Cinderella Girls was the first mobile game spin-off series for the idolm@ster franchise. It is currently only playable in Japanese and Korean language but if you're still interested in playing you actually can by signing up for mobage. There is an app available on both itunes and googleplay services which can be downloaded using a VPN. The same method that I wrote about for downloading Million Live onto android phones can also be used for Cinderella Girls. Link Here
As for how to play, well, there's probably no perfect guide out there but project-imas wiki has a good foundation to start with. Keep in mind you do need a Japanese phone number to verify your account in order to unlock full services but it is still playable if you choose not to. If you've played any other mobile card game before though it's not much different; click your phone over and over and spend money gacha draws to love your idols.
You can find samples for just about every idolm@ster CD on the official columbia website.
Unlike the original 765Pro and Million Live!, not every idol in Cinderella Girls is voiced. As a matter of fact there are over 200 idols in Cinderella Girls so it would be an amazing feat if that was ever achieved (don't get your hopes up). But that also makes it quite significant whenever new music is actually released for Cinderella Girls since that's usually when an idol gains a voice for the first time.
As you can see in this link, there have already been 30 solo CD series for Cinderella idols with 5 more planned to be released in the near future. Idols chosen to gain voices and songs are sometimes chosen by fans in popularity polls and contests. Furthermore, the jewelries series contain collaborations between idols of the same type. In Cinderella Girls, those three types are Cute, Cool, and Passion. Producers of Cinderella Girls often identify themselves as a Producer of one of the three types (CoolP here!).
Cinderella Girls has now had two major live concerts in Japan, the first of which was recently released onto Blu-ray and DVD. You can see 3 great preview PVs featuring Cute, Cool, and Passion idols for it thanks to columbia's youtube channel.
If you love Onegai! Cinderella and want to learn the calls to it, there's also a great tutorial video for learning them.
By now there's a good 30-40 seiyuu working with Cinderella Girls. The best way to get to know the main ones however is probably by listening to the radio shows Dereraji and Derepa however.
Dereraji is hosted by Fukuhara Ayaka (Shibuya Rin), Ohashi Ayaka (Shimamura Uzuki), and Yoshimura Haruka (Jougasaki Mika). Derepa on the other hand is a duo radio by Hara Sayuri (Honda Mio) and Aoki Ruriko (Tada Riina).
And I know seiyuu radio just doesn't work with a lot of people out there and if you're not already listening to seiyuu radio than odds are me telling you about it won't make you. Still, if radio isn't your thing then you can also see them during the upcoming Nico Livestream broadcasts for Cinderella Girls.
This live broadcast next week will allow you to watch the 2nd episode alongside with the seiyuu and staff. You can find the future ones in the description. Keep in mind these do require a VPN to watch outside of Japan. If you really have no means of enabling that, in all likelihood it will be uploaded to nico nico douga shortly after.
Last but not least I'm going to point you in the direction of my friend's tumblr who has profiled several of the Cinderella Girls seiyuu now because they're incredibly helpful for English-only speakers wanting to know more about them and I'm a lazy guy who won't do anything like this himself.
That's all for now. As for my actual thoughts regarding the anime... I'll save it for a better time. Oh, but Producer is love!