So I recently discovered and quite to my surprise that there is a Jpop station available on 'iheartradio' (website and smartphone app), KORL 97.1 out of Hawaii - http://www.iheart.com/live/J-Pop-971-6386/
(It took me awhile to find it because it doesn't show up with keywords like 'japan' or 'japanese' or even 'jpop'... I think it does respond to 'j-pop' but I actually found it by browsing to 'world music' not particularly searching for a j-pop station but just to see what was there and be pleasantly surprised.)

Access to streaming radio out of Japan is kind of limited as far as I can find, and I'm definitely enjoying this station more than searching around through radio stations that only stream part of the day or play 3 American songs for every japanese song...
However, if anyone has recommendations for other streaming sources of Japanese-language music, I'd be glad to hear about it.

http://www.simulradio.info/

is probably what you're talking about. All of the stations there are community stations, so they don't have full broadcast days, and their format is really "All Over the Road." One minute, it's an old Eagles song from the 70s, the next it's enka, and it could be rap after that. If you think of it as background music for a local bar, it works (kind of). But if you try to listen to it actively, you may go crazy.

If you want to listen to anything in Japan that isn't community radio, you'll need a VPN and you'll have to use radiko.jp (because we can't have outsiders listening!)

Ahh, VPN isn't a problem at home (my sub is expired right now but my usual provider isn't expensive), but I hadn't heard of radiko.jp before. I dunno about VPN on my smartphone... it's supposed to be possible but I've never done it. Could be a worthwhile adventure! Having a Jpop station is nice and all, but having access to Jrock and Enka too would be even better

simulradio is the one I was mostly thinking of, although some others provide the same stations as simulradio (I don't know if they just relay simulradio or use the same methods or what, but it's the same set of stations.)

This list of radio stations may be useful. (Go down to the bottom of the Kantou region to find Tokyo radio stations.)

Tokyo FM uses radiko, too. There aren't a whole lot of radio stations in Tokyo, but the big ones all use it. (Dunno if TBS radio does or not. I can't remember.)

Radiko is pretty aggressive in blocking VPN, it seems. I tried accessing it on my tablet through TorGuard's Tokyo servers, and I got showed the gaijin door. ;_;

I guess JASRAC is paranoid that we may hear their secret music? It's really weird. I can listen to just about any other country's radio stations, but only Japan is a royal pain in the butt about it.

Thank you for the iHeartRadio tip, it took some time to get it working for me here in Europe, but I eventually managed with a VPN and fresh playstore account

I also found that there are plenty of JPop radio stations on TuneIn radio http://tunein.com/. It also has an Android app, so I use it to listen on my smartphone. TuneIn includes the station mentioned in the original post, and I have no problem accessing it from a europe, without VPN. Just search for JPop or Japanese and you will find a relatively large list of (likely) community driven stations. Example of what I am listening to now: http://tunein.com/radio/J-Pop-Project-Radio-s225524/. There are also a couple of stations that broadcast from Japan, but not all of them load for me.