install OpenSSH on iPhone and the default password for the default accounts

You can install OpenSSHd from Cydia. Search OpenSSH and install it. After that, you can connect to your iPhone via ssh, there are 2 users created for you, mobile and root. The default password is alpine, you should change that as soon as possible.

Example:
huangxh@agamemnon:~$ ssh mobile@10.6.175.246
mobile@10.6.175.246′s password: [alpine]
Huang-Jiang-Bins-iPhone-3:~ mobile$ passwd
Changing password for mobile.
Old password: [alpine]
New password: [your password]
Retype new password: [your password]
Huang-Jiang-Bins-iPhone-3:~ mobile$ su
Password: [alpine]
Huang-Jiang-Bins-iPhone-3:/var/mobile root# passwd
Changing password for root.
New password: [your password]
Retype new password: [your password]