And in the future, you can install apps from .deb files.
However your iPhone must already been jailbroke (see tutorial to untethered jailbreak with Corona, Redsn0w or PwnageTool) before installing .deb file.
So let's install deb files now, but before doing so, read the requirements below and then follow them all in order to complete the whole processes.
1. Download fugu -- here is the link.
2. Open SSH your iPhone For Mac Or Windows.
How To Install deb files via Cydia
Step 2: Enter your iDevice IP address in the connect to: and in the username: enter root. Afterward, click Connect button.
Step 3: Enter password: alpine if asked. Click Authenticate.
Step 4: From Fugu toolbar, click Go To (BUTTON).
Step 5:Input /var/root/Media as the location to Go To. And choose Remotely, continue by clicking on Go button.
Step 6: Create Cydia folder by clicking the New Folder button on Fugu toolbar:
And name the directory: Cydia. Don't forget to choose Remotely before clicking on Create button.
Step7: Click twice on Cydia folder you just created to enter.
Step 8: Create AutoInstall folder, if you don't have one in the following path: /var/root/Media/Cydia. Do so by clicking on the New Folder button on Fugu bar:
Name AutoInstall as its name. Choose Remotely, before hitting Create button.
Step 9: Double click on AutoInstall, to get in the folder.
Step 10: Now get into the DEB files location you want to install from the Fugu's left pane.
Step 11: Drag the DEB files from the left to the right.
Step 12: Now power on and off for two times after the file entirely copied.
Step 13: Now in your Homescreen and Cydia Installer you can see the recent installed applications and congratulation!