Can Cisco router 877M have the features or capability to use VOIP or Unified Communications technology?
The 877 does not support Unified Communications manager express which is the IP PBX provides call control. The 877 does provide the appropriate level of Quality of Service to successfully pass voice traffic to a centralixzed IP PBX running on a server. You didn't give a size of your company so it is hard to recommend what to consider.
The SBCS would be a complete and robust system with telephone call processing, voicemail, automated attendant, and conferencing functions.
The pricing for these systems has just recently been reduced and there is a nice financing option available. You can have a look at the SBCS here http://www.cisco.com/cisco/web/solutions/small_business/products/voice_conferencing/smart_business_communications_system/index.html
On the get started tab on that page you will find info on financing.
In the Cisco Small Business portfolio, we offer Smart Business Communication System (SBCS), which is a suite of products providing UC to the small biz.
This includes Remote Teleworkers, namely the 871W ISR and the SR520, if you need ADSL interface. This includes GUI Management and configuration using CCA (Cisco COnfiguration Assistant). This suite of products are Engineered and tested to work together, and supported that was as well.
You can introduce other products and attemt to interoperate them, but you will be drifting away from the value added by sticking to the designs and best practice deployments we recommend.
More on 8xx ISRs:
More on SR520: