Dear Sir,
Our company has over 8 years of experience in VoIP area in general and working with Cisco equipment in particular. Our team consists of highly qualified and professional engineers, most of them have Cisco certification (CCNA, ICND, CCAI, CCNP). We have been working with all the equipment you mentioned such as 2811 router, 7970 and 7912 IP phones etc. We use Cisco Catalyst and Cisco 3620 router in our own network and there will be no problems to configure your Cisco environment. If you are interested, please contact us at your convenience. Thanks and regards, VoIP Experts.