I replaced my home landline with an Asterisk box running on a Supermicro Atom D510 mboard, specifically PBX in a flash, which is the Cliffs' notes version of FreePBX. FreePBX is based on Asterisk, but provides a spiffy web interface for configuration that's more advanced and free-er than the others. That said, you'll still need to be comfortable at the command line on Linux and a text editor such as vi.
With Asterisk, you can do voicemail, have your voicemail emailed to you, have multiple boxes, pay $1.50 per month for a phone number plus $.01/minute for calls with a SIP provider such as Vitelity. You can have conference calls (you'll need to pay $10/channel for g729 if you want to scale at all on home bandwidth, though.)
You can have ring groups, different extensions, etc. I have one for emergency late-night network issues, which only those with the secret extension can access to wake me up.
There's an unlimited number of stupid tricks you can do, but you'll need to learn the difference between trunks, routes, and dial plans. That said, it's pretty cool. But then you'll want to buy Aastra SIP phones, which come with open-source phone applications, so it will cost you more. If you want to light up your in-house phone lines, it's $200 for an FXS card. If you want to use an existing landline as a trunk, it's $200 for an FXO card. (Double check which is which before you buy because I can never remember which is which.)
The best part about running your own PBX is that (1) you can send telemarketers to voicemail hell and (2) it's trivial to fake callerID, which helps with (1).
9. Place it on a train.
8. Place it on a freighter carrying electronics to be recycled in China.
7 Place it in your carry-on luggage and watch the fun at airport security.
6. Dial 911 and tell them you've found a bomb on your car. Invite TV news crews to come watch the fun.
5. Give it to your local ACLU and tell them to make the FBI prove it's theirs before handing it back.
4. Pretend you don't know it's there, and drive to as many Tea Party events as possible.
3. Build an autonomous flying drone capable of carrying it and program it to fly around in circles all day.
2. Hack its logic to input arbitrary coordinates and make virtual visits to places you've always wanted to see.
1. Pretend it's not there and go on a tour of the most patriotic American landmarks to demonstrate your loyalty to the United States.
Basic firewalling is not complex. Defense-in-depth and creating compartmentalized networks for each layer in each application in your worldwide network gets complex no matter what tools you use. The trouble with unified threat management is that no single vendor is going to catch everything.
The single most effective thing you can do to secure your networks is to start by denying all ports inbound AND outbound. Then open up only those ports required for your business. Use an authenticated proxy for client web traffic, and your users don't have to connect the Internet directly any more.