Don't be too put off by the term 'hack' (though, in essence, this is what it is) - think of it as freeing your Symbian phone from the tight installer controls put in place by Nokia back in the day. Of course, while the OS was being actively maintained (e.g. with security patches) it made absolute sense to 'stay within the reservation', avoid hacking and use the official Nokia Store for software. But with the Store about to close for the last time, with all patching long since stopped and with support itself getting on for non-existent, there's more cause to experiment and start thinking about software from other sources, regardless of the lack of any approval or certificate.
Of course, this brings an implicit danger that you'll be installing something malicious, so exercise caution as you go and don't go installing lots of new applications in one go. And do backups as you go - but the idea of freeing up a smartphone in this way, independently from the OEM, is quite appealing.
Noting that you'll need to be quite technical and know your way around a file manager, from the article at Symbian Developers, quoting the instructions for a Belle FP2 device (like the 808):
1. Download and install this application to C:\ drive: http://symbian-developers.net/wp-content/uploads/Nokia-Belle-FP2-Hack.sis
2. After the installation, SafeManager should launch. If not, launch it from the menu
3. Three popups will show up. Select No to all of them
4. Click on Other, and after that on FileMgr
5. Now open FP2hack folder in E:\ drive, select the updatedswicertstore.dat file, open the Options menu and select Copy
6. After that, go to C:/resource/swicertstore/dat/, open the Options menu and select Insert. Enter the code shown in the popup and press Ok. When it asks you to insert the file, press Ok, and select Yes when you’re asked to replace the old file in the folder.
If the folders don’t exist, just create them.
7. Download and install RomPatcher+ v3.1 for Belle FP2 from this link: http://symbian-developers.net/wp-content/uploads/RomPatcherPlus_3.1_FP2.sisx
8. After it’s installed, launch RomPatcherPlus from the menu
9. Select all of the patches (Install Server RP+ v1.7 and Open4all), open the Options menu and select Add to auto
On the source page there are similar instructions for older Symbian smartphones, so go look.
Me? I'm firmly in the Delight custom firmware camp (this also includes the installation of any application, out of the box), but I wanted to give some credit to the slightly fiddly method above since it doesn't force you to wipe your device and start from scratch in the process.