911 is handled via a PSAP ( Public Safety Answering Point )
For example, in Sacramento County's unincorporated area, the Sacramento County Sheriff's Dept answers all 911 calls made from landline (home) telephones. If the emergency requires Fire / Medical aid, the Sheriff's 911 Dispatch then transfers the call to the Sac Regional Fire Dispatch center. The Sac Fire Dispatch Center does not handle direct dial 911 calls, they get all their 911 calls as transfers from other agencies or direct dial to their 7 digit emergency line. 916-228-3000
If the 911 caller is within the incorporated area of Sacramento - The City of Sacramento, landline 911 calls go to the Sacramento Police Dept Dispatch Center. Just like Sac Sheriff, if the emergency is Fire/Medical, they will transfer the caller to Sac Regional Fire Dispatch.
CHP has several PSAP's and handle "most" cell 911 calls in California. If a caller connects to a cell tower that is "assigned" to CHP, their dispatch center receives the 911 call, and either handles the incident or transfers to the appropriate agency.
Some cell towers are assigned to a PSAP other than CHP, such as Elk Grove. If you call 911 within the City of Elk Grove, most cell towers in that jurisdiction will route to the Elk Grove Police Dept 911 Center. Again, if the emergency is medical/fire, Elk Grove PD will route the caller over to Fire Dispatch.
There are a lot of variables for PSAPs. Some jurisdictions, such as Isleton Police Dept contract their 911 services to Solano County Sheriff's Dept. Even though the City of Isleton is located in Sacramento County, residents that call 911 will be received at the Solano County Sheriff's Dept 911 center.
VOIP ( voice over internet protocol ) is a bit different and most 911 calls from a VOIP user will route to the appropriate 911 center. In some cases, VOIP 911 calls are handled by a non-law enforcement call centers which could be located anywhere in the United States.
The issue with Text messages is with cell towers. Obviously your cell phone connects with a radio tower, and your text message will transmit via this cell tower. The cell towers location would determine where your text message is routed. The most significant obstacle is that a 911 dispatch can't really "interview" the caller. The party sending the text message must provide detailed information, in a clear and concise format. Calling 911 and getting the appropriate service requires information, and the VAST MAJORITY of citizens calling 911 have very little experience in dealing with emergency situations and public safety services. One could also conclude, that if a party can call 911, providing a lengthy text message with necessary information, one could actually just call 911. The other issue is that the 911 caller can only assume that their text message or messages were received in their entirety. Also, the reliability of text messaging is nowhere close to that of connecting a phone call.