This should be implemented

Q u o t e:
Blizzard needs to add a "Home channel" feature on Battle.net for DIablo II for those of us who prefer to stay out of public channels away from the spambots, and for those of us who have clan channels and whatnot.

Having to join whichever channel everytime you enter chat from logging in or switching characters is highly annoying after the first 1000 times you do it.

I actually implemented this feature in 1.13, but unfortunately we didn't get this into the patch notes. You can set a Diablo II registry key to the specific channel you want to join.

Computer\HKEY_CURRENT_USER\Software\Blizzard Entertainment\Diablo II

Type: REG_SZ
Name: Default Channel

Set the data for this string value to the channel name you'd like to join. Now when you enter Battle.net chat, you should be in the channel of your choice. If you do this, you will miss the intro information printed out by Battle.net, such as how many users are using the Battle.net service and when your last logon was. This may also hide any indication of previous failed login attempts on your account.

It should be noted that editing your registry is definitely not for everyone. If you don't feel comfortable doing it, please don't.