It's easy, it works very well with my phone line (it doesn't require an internet connection) I can receive calls from people who are not in my contact list as long as they have their number stored into geniusfax! The only problem is that sometimes when you try sending something or receiving something while someone else has already sent/received something using this program there will be slight delays of up to five seconds before things get updated for others.
This isn't really much but if your having any problems please let me know so we may fix them together. My business uses geniusFax because i am able to communicate easily between our office via email etc.