JMP will support 911 emergency calls for new users if a sufficient number of JMP users (a dozen or more) commit to adding $2/month to their JMP payments for 911 support (those who don't want 911 support won't see a pricing change). By default 911 is not activated for JMP users, primarily because the majority of users use cell phones that obviously don't have a fixed location and thus storing some street address in JMP's database would be counter-productive.
It is recommended to use the phone's built-in emergency calling which goes through the cell carrier and enables the carrier to fill-in the location information based on cell triangulation. This does not require an active cell plan - only a cell phone - as all carriers (at least in North America) are legally required to let you place emergency calls on their network whether you're a customer or not (and your phone will automatically connect to their network to place an emergency call).
If you are using JMP.chat at a fixed location (e.g. with an ATA) then there are some providers that provide E911 service only. GV 911 (operated by BulkVS) offers such a service for $12/year. This service routes your 911 or 922 (test number) call to them via JMP.chat, and then your caller ID is used to look up the phone number and address to pass on to the emergency call center. You will need to be able to configure your ATA to forward 911 and 922 to the GV911 routing numbers.