| Business | Phone |
| Ats Communications Inc 2500 Annalisa Dr # 200, Concord 94520 | (925) 602-1500 |
| Contra Costa Phone Svc 1746 Sapling Ct, Concord 94519 | (925) 671-7776 |
| Smart Homes Usa 1820 Arnold Industrial Way, Concord 94520 | (925) 827-3484 |
| A-1 Data Inc Concord 94520 | (925) 603-5200 |
| Applied Communications 5161 Clayton Rd, Concord 94521 | (925) 692-1500 |
| Comcinc 4030 Pike Ln, Concord 94520 | (925) 849-1400 |
| Elite Telecommunications Svc 5295 Ambleside Dr, Concord 94521 | (925) 521-9222 |
| Jck Communications 1717 Solano Way # 19, Concord 94520 | (925) 689-7787 |
| Mci 1714 Colfax St, Concord 94520 | (925) 675-6400 |
| Spirent Communications 2300 Clayton Rd, Concord 94520 | (925) 288-0110 |
| Warner Communication Systems 1155 Basswood Pl, Concord 94521 | (925) 672-9892 |