Microsoft has officially released its next-gen Windows Phone 8 operating system, but those still using Windows Phone 7 are still anticipating the long awaited 7.8 update. The upgrade is said to be the last for Windows Phone 7, and evidence about what the update will include has continued to mount.

GSM Arena reports that a version of Nokia’s Lumia 510 running Windows Phone 7.8 has just been spotted, and according to WPCentral a brochure highlighting the update’s features had made its way to the Web.

A Finnish user reportedly snagged a Windows Phone 7.8 brochure from a shop in Finland and snapped a photo of the advertisement. The brochure is written in Finnish, but WPCentral was told that it states the following:

“…there will be more theme colors to choose from, it also says that there will be more than the new start screen. And what’s really important is that it confirms that there will be another update after the WP 7.8 update.”

This may come as a surprise to some, considering that 7.8 was thought to be the last update for Windows phone 7 users. However, this is the second indication that Microsoft will release another update after 7.8. Earlier in November an allegedly leaked document from Nokia hinted that there would be a post- Windows Phone 7.8 update. Since Windows Phone 8 isn’t available for legacy devices, Windows Phone 7 users should be happy to know that Microsoft may continue to roll out software updates for their handsets.

In addition to the new theme colors that are believed to come with Windows 7.8, WPCentral has also learned the software’s build number: 7.10.8858.136. The Windows Phone news site does not specify its sources, but says that it is a “confirmed build number for at least some of what Nokia is working with.”

The Nokia Lumia 510 that is reportedly running Windows 7.8 also revealed some interesting tidbits about what Windows Phone 7 users can expect. Microsoft appears to be mirroring a Windows Phone 8 experience for its legacy device users, as the 7.8 update is expected to bring the following: resizable Live Tiles, revamped system apps such as Xbox Games and Microsoft Office, 10 new theme colors, a new boot screen matching Windows Phone 8 and Live Lock Screen Wallpaper.

It’s important to remember that information about these features has not been confirmed by Microsoft and comes purely from a Nokia 510 believed to be running the update.  Microsoft appears to be relatively tight-lipped about Windows Phone 7.8, as the company recently issued a statement to Tech Crunch saying, “We have made no further announcement on this but hope to share more details in the near future.”

This response comes just after Microsoft blogger Paul Thurrott called the company out on their silence concerning Windows Phone 7.8, as he wrote the following in his Windows blog post:

“When Microsoft announced Windows 7.8 in June, I knew it was too good to be true. At the time, it seemed like Microsoft was throwing a bone to disappointed early adopters who would not be able to upgrade their existing handsets to Windows Phone 8. Today, it just seems like a slap in the face… Today, almost exactly one month after the Windows Phone 8 release and over 5 months after it was announced, Microsoft has never really publicly discussed Windows Phone 7.8 again nor has it hinted at when it might be released.”

While the release date for Windows Phone 7.8 remains a mystery, this mounting evidence can only prompt some to hope that it will launch soon. Check out the video below to get a glimpse at the Lumia 510 allegedly running the update.