The APN is needed to make software such as VeriChat, WebMessenger, Reqwireless, midpssh, MobileSSH, etc, working on Rogers. The APN is not necessary if you are on a BES with MDS.
Without an APN and without a BES, it doesn't work. Unless Rogers has recently changed the configuration or you are using a new BlackBerryOS that autoconfigures the APN.
Also, this is an old post. The latest Configuring Internet is located in my BlackBerry FAQ link below. I have edited the post to point to the most recent version.