I highly recommend http://FreedomVoice.com - they're great guys on the phone, will work with you to get the kind of number you're looking for, and although the setup fee is a bit of a setback, it's been a great, reliable system. I hired a voice actor who got me MP3s for our "press X for..." menus and it was a 10-second process to upload them on FreedomVoice's control panel, and it instantly went live.
Essentially, for $10/month, we have a professional PBX-like phone system like any Fortune 500 business.
There's a major difference between a Virtual Auto Attendant which is what you have Vs. a true HPBX phone system. With a HPBX phone system which is what most companies within the SME market use these days the equipment required to deliver such as service would consist of VoIP phones such as Polycom, Cisco handsets, ATAs, a POE switch, Cisco router, and a T1 connection which is typically included by the provider. Depending on how many simultaneous calls you want to handle at any given time a DSL/Cable connection would be ideal for 4-6 concurrent connections.
With your typical Virtual Auto Attendant the service simply terminates the call to whatever device you have configured, a land line, mobile device etc.. However, you're absolutely correct, having a virtual auto attendant is certainly worth the 10/mth investment but to compare it to a HPBX system would not be fair. Another thought to keep in mind is, will you actually be able to answer the calls? If not, this could also produce a negative outlook on your organization.