Judging by the information provided by the tipster, the former is a dual-SIM handset while the latter is a single-SIM device. Both of them have Wi-Fi on board, and it won't be surprising if they are full-touchscreen devices, just like the members of the recently unveiled Asha touch trio. The rumor is accompanied by a couple of photos showing a touchscreen handset with a Nokia logo on it. Unfortunately, not a whole lot of the phone can be seen as it is inside a strange-looking case, possibly so that it doesn't attract prying eyes.
Of course, you should file all of the above information under rumors and keep it there until we get more evidence in support of the Asha 308 and 309's existence. After all, the leak might be a fake, or the new models may simply be variants of existing ones tailored for the Asian market.