Basically what the title says: a chart that tells which versions can connect and which can't.
(note: on this chart, all instances of "V4" can also be used for "V4.5")
HOW TO CONNECT CERTAIN VERSIONS
While some of the Tamagotchi pets do not say if they can connect to more recent versions, they can. This is how:
~Connecting a Version 2 to a Version 3 or 4/4.5~
On the connecting options for the V2, select "Version 1"
On the connecting options for the V3 or V4, select "Other".
~Connecting Versions 2, 3, and 4/4.5 to the Keitai/Akai series Tamagotchi's~
On the Version 2, select "Version 1". On V3 and V4, select "Other"
On the Keitai/Akai select "Tamagotchi Plus" (symbolized with a + next to Japanese text).
~Connecting Version 4 to Version 4.5~
On the V4, select "Ver. 4", and select what option you'd like to use (Game, Present, or Visit).
On the V4.5, select "Ver. 4/4.5" and select what option you'd like to use (Game, Present, or Visit).
~Connection Version 4/4.5 Connecting Glitch~
For whatever reason, the V4 and V4.5 both are picky about connecting. Sometimes, when you try to connect them to any other Tamagotchi, they will just say "FAIL" instantly.
To correct this glitch, reset the V4 or V4.5, download your character, set the correct date and time, and try again.
~Connecting Music Star/V6 to V5/Famitama or V5C/V5.5/Royal Famitama~
On the Music Star, select "Others" and wait on the Standby screen. DO NOT PRESS B.
On the Family pet, select the first option, then "Game", and then press B.
~Marrying Music Star/V6 to V5/Famitama or V5C/V5.5/Royal Famitama~
After building up friendship levels on both toys to their highest possible levels, start the connecting process. But for the Family pet, select "Marry" and then "Give".
The adult will disappear from your Family toy, and appear on your Music Star as Nazotchi. You will receive an egg with the new baby, and Nazotchi will stay and live with your Music Star.
~Music Star/Family Pet Marriage Glitch~
Please be careful when marrying your V6 with the Family pets.
The Music Star will take about twice as long to build the friendship level than the V5 (or all Family-style pets in general). The Music Star's Friendship Meter consists of 8 stages: four static faces, and then four smiling faces. Be sure to have all four smiling faces before deciding to marry the V5.
If you don't do this properly, your Music Star will refuse to marry, but the V5 will accept - sending a character away and leaving you with one less character and no way of getting it back.
PLEASE REMEMBER TO PRESS "B" ON THE "STAND-BY" SCREEN TO SEE "CONNECT", OTHERWISE YOUR TAMAGOTCHI'S WILL NOT CONNECT!
UPDATE 12/26/09: Added V6 Info.