Hi Maximo,
Yes, the 881V would work great for a 2 person office with expansion to 5 users as you noted;
Q. Is Cisco Unified Communications Manager Express supported on the Cisco 880 Series voice models?
A. Cisco Unified Communications Manager Express is supported on the Cisco 881V and 887VA-V platforms with a 5-user Cisco Unified Communications Manager Express (Cisco Unified CME)/Cisco Unified Survivable Remote Site Telephony (Cisco Unified SRST) license upgrade. The Cisco 880 Series SRST models have SRST support only.
Q. Which version of Cisco Unified Communications Manager Express is supported?
A. Version 8.6 or later.
From;
http://www.cisco.com/c/en/us/products/collateral/routers/800-series-routers/qa_c67_458826.html
Cheers!
Rob