Emergency Medical Service (EMS) in Lagos?

Critical Rescue International, "Nigeria's First National Advanced Medical Paramedic Company", is probably what you're looking for.

Subscription to their service is available to individuals and corporate organizations, but they also run the Vmobile 199 Service (formerly Econet Crisis Center - see poster).  If you're on the Vmobile Network, just dial 199 whenever you need emergency medical services.

To learn more about the Vmobile 199 Service, visit:
   http://www.vmobile-nigeria.com/social-responsibility-199.htm

To learn more about Critical Rescue International, visit:
   http://www.crinigeria.com/ or dial 0802 888