I have alot of experinece with OTM. Started with 2.1. It is much more user friendly than using the command line for programming. If you don't know the command structure of the LD's then don't even attempt it at this point.
The current version of "OTM" is now called Telephony Manager 3.1. It is web/browser based for station administration, IIS based. Making changes to new and older phones alike is rather easy compared to the command line. The PC would be loaded with the software and it would be connected to Nortels internal network (ELAN). Yes you need a Dongle as mentioned, its a USB device that is from Nortel for licensing purposes.
Log onto Nortel's web site and download the following docs for a comprehensive understanding of the product:
Telephony Manager 3.1 Installation and Commissioning - NN43050-300_01.05_TM31InCom Telephony Manager 3.1 System Administration - NN43050-601_01.02_TM31SA. Fair warning, if you plan to put your server on your LAN it can be an absolute BEAR to deal with. Especially if you apply and internal security templates. This software is extremly sensitive and picky! Read the documentaion carefully and follow it to the letter. If you can avoid putting on security templates then do it, you'll make your life alot less stressfull. Important note Do not load it on a Win 2003 Server R2. It will not work. I found out the hard way and had to reload the entire OS and TM 3.1
Use Win 2003 Server Standard edition and follow the the configuration in the docs to the letter. There are alsoPEPs and SU's from Nortel to update to the lastest patches and bug fixes. The web interface has a comprehensive help index covering many areas including the LD's. It's a good way to break into the command line structure.