These codes are included in all builds.

Numeric Code	Alternate Code	Function
217	up, down, right, go	Go to phone settings
32768	home, back, up, down, go	Clear flash NV RAM (including tellyscript, dialing options, TV listings, etc.)
080813	home, back, down, up, go	Clear serial NV RAM (emergency 800 number)
07081969	home, right, left, back, go	Force flash download
024995	-none-	Boot into diags

These codes available in Production Builds, only with Client 1.1 (or later)

Numeric Code	Alternate Code	Function
411	home, back, recent, go	Shows technical information for the box
7264	scrolldown, back, home, scrollup	Clears tellyscript (not dialing options, etc.) - used to be a bug in classic clients that made this secret code work improperly, but with the forced upgrade to client 1.4, 7264 now works as expected.
7265	unknown	Another version of 7264, not currently in general use.
77437	back, back, up, up, go	"Spooky Dialing Options"
18004693288	up, down, left, right, up, down, left, right, go	Force signup again
0000	unknown	Do MessageWatch mail check (unsupported, but seems to work)

These codes are in non-production builds only:

Numeric Code	Alternate Code	Function
93288	left, right, left, right, go	Boot into connect
90210	-none-	Boot into tourist mode
031158	home, back, left, right, go	Starts up the Kiosk Demo mode.
061185	-none-	Turn off Demo mode on a retail box. If in retail group on the service, demo mode will be reset when it connects and will go back to demo.
0000	-none-	Check MessageWatch, Fetch Video Ad. Terminal must have connected to the service, with MessageWatch activated, at least once since it was plugged in. Box should power up, check for mail, and fetch a video ad.

These codes work only on LC2 units

Numeric Code	Alternate Code	Function
8675309	unknown	Boot into Mini-Browser for downloading Boot or App ROMS (primarily development use for flashing BootROMS)
314159	unknown	Disable secure download checking (used on pre-2014 builds as they don't support encrypted downloads)
159753	unknown	Delete Disk Cache
48627931	unknown	Delete Group Database - the client and service often want to check to see if broad groups of files are present and valid. This is done by checking groups, instead of individual files. Sometimes, the group gets out of sync with the individual files. This code destroys the group database, so the service will download everything again (IR, EPG, etc.), or at least take a look at individual files.
7445000	unknown	Delete Video Ads from Disk
55325532	Unknown	Delete Everything But The Browser

These codes work only on internal builds of LC2 Internet terminals

24682468	unknown	Do Not Use Unless You Know What You're Doing! -- Trashes the browser image
13571357	unknown	Do Not Use Unless You Know What You're Doing! -- Writes a few spare bytes into NVRAM, so the checksum will fail
7225000	unknown	Blanks TV listings -- deletes current set of TV listings
7335000	unknown	Blanks IR Blaster Codes -- deletes current set of IR blaster codes
1111	unknown	Forces Data downloads in non-debug, non-production builds

This may only work in Export Builds (not clear)

46725

unknown

Changes to and from PAL size -- If in PAL size (640x480), go to NTSC (normal mode). If in NTSC, goto PAL size

By way of more detail, the 8675309 code isn't likely to be used for customers, as production units should have a burned-in bootROM, as opposed to the flashable bootROM from development boxes. It's conceivable that it might be used on a box with its client corrupted at some point, but primarily it's used for downloading bootROM.

LC2 boxes can engage in secure boot and app ROM downloads. This plugs a security hole that an individual could induce a box to download a fake version of the client (if someone could write one to fool the client). Early LC2 builds (before 2014) aren't capable of dealing with the encrypted download, hence must be flashed using secret code 314159. May also be useful eventually for customers if for some reason the encryption is causing problems with the download.

32768: 2^15, largest signed 2-byte integer
07081969: Joe Britt's birthday
411: Information
77437: Spies (a Rubin venture) spelled out on a telephone
18004693288: 1-800-GO-WEBTV on a telephone
90210: Zip Code for Beverly Hills
031158: Dave Anderson's birthday
8675309: The phone number from that Tommy Tutone song (Jenney's phone number)
314159: The number pi