If I am not mistaken, the $100 activation comes included with:
1. Pre-configured VoIP ATA (I purchased PAP2T for $56)
2. FreePhoneLine ATA account
If you already have an ATA like many others I would assume, then it would only cost you $50 to setup an account (unlock) with FreePhoneLine. It is free in a sense that once you receive your account info (unlock key), then it becomes free for as long as you want. I pay no less than $10 monthly for VoIP.ms. Obviously, FPL would be "FREE" for me after five months with them.
Also, if you don't intend on using an ATA, then FPL is ABSOLUTELY FREE. I already have a number with them and I plan on using it with my cell as I will be getting a new cell phone with unlimited incoming