This is an informal discussion based on personal experience from late 1990s to present day in the United States during various non-local domestic incidents. Always follow advice from authorities as priority.
The phone tree has become derided as a first choice for organizational awareness. For more informal situations like connecting family groups spread out across states and regions, an informal phone tree can be a backup choice. A key element of this approach is that before a crisis emerges, give/collect phone numbers to several people in a city or region. At least some of these should be people more on the fringes of your social network but still connected in some other way (perhaps a relative in another city of someone you know locally). In this way, the remote and local connections to you are motivated to keep the chain going since there is a friend or family connection beyond yourself. This technique is ideally copied across each ’node’ of the phone tree.
Instead of blast group SMS text messages, which can get delayed and become overwhelming in alerting the recipients with a flood of messages, a phone text tree allows each node to decide which subset is best served by passing on that message. For example, the more maker-savvy folks may appreciate new info on fan filter box construction, while those needing particular supplies may appreciate knowing a store or website suddenly has availability. Blast group text message sent informally even in family groups may suffer from a cascading effect where too much chit chat causes recipients to “tune out” their attention and miss more important messages.
A key idea is to target messaging from each human node using their knowledge of connecting human nodes. This is like a Mechanical Turk for urgent text messaging. The more targeted nature of the messaging incentives spreading more carefully curated information.
Government authorities can broadcast text messages using WEA to cell phones–I have generally had positive experiences with this during severe weather events. The non-WEA, non-CMAS SMS text alert services commonly used by universities and other campuses too often experience delays, where one person may receive an alert minutes after others in the same vicinity.