His name escapes me right now but the http://www.ciscoblog.com/ has an entry about the coolness of the Cisco 1861 ISR. This little thing does it all. Voice, firewall, VPN, LAN switch with POE and wireless through an HWIC. It can also operate in SRST mode which is probably an even more attractive model. Unfortunately it's not all roses. The price is a list of $5500 with the wireless. Add in phones and you're pushing well above key system pricing. Ok, it does it all and you need to factor that in. Consider the cost of an ASA 5505, an AP and an Ethernet switch on top of that key system and it gets a little closer to parity. Plus you sacrifice integration and features with the separate components.
A better alternative for small sites might be the UC 520 Express. Lists for $4500 with the wireless. It doesn't have the expandability of an 1861 as the software is somewhat locked out, but the price point gets better for small businesses. At such small phone counts a $1k swing in price makes a huge difference in per-phone cost.