Android devices can be used as network cameras. There are various apps for Android that can provide a video stream, and some that record videos which can be imported into a surveillance system. It should also be possible, by rooting your device, to use existing linux programs to stream camera video.
Via forums, users report the easiest setup is with the official Android Play store's IP Camera app. This app is proprietary however.
I've tested a few Android phones with apps from F-Droid and received mixed results.
It is recommended to use apps from a trusted source. Some apps will serve ads, others will pull your personal information. Choose wisely.
The following apps are from F-Droid. F-Droid Provides a repository of free and open source software for android. 
Supports Mjpeg and audio streaming. Built-in web service to see the video via browser on a PC.
Version 1.61 JPEG images are available at http://<ipaddress>:8080/stream/live.jpg ZM does not seem to work at pulling the images directly. Pull the files via a script populate them in a local directory and you can get 1FPS in ZM.
- $ watch --interval .2 "wget -q http://<ipaddress>:8080/stream/live.jpg -o /dir/you/want/to/put/image/download.jpg && mv /dir/you/want/to/put/image/download.jpg /dir/you/want/to/put/image/live.jpg"
- ZM Settings:
- Type: File
- Maximum FPS: 5
- Address: /dir/you/want/to/put/image/live.jpg
Not sure why ZM doesn't display frames faster than 1 FPS when the files are clearly updating faster. You move the file so that there are not incomplete files due to wget overwriting the previous file.
Provides HTTP webpage and RTSP stream. RTSP stream is accessible from rtsp://<ipaddressofphone>:8086 Stream is viewable in VLC and recordable through VLC, but as of yet is not viewable in ZM.
- RTSP Server: enabled
Then stream from VLC.
This application provides an MJPEG stream, from its web server. Does not work on all devices. This applications is designed to be used for occasional snapshots (hence the name 'webcam') and is not designed by the author as an IP Camera application. However it should be possible to get very low FPS with this application such as .2 FPS) into Zoneminder.
- Upload: SD Card (no sdcard needed)
- Refresh Time: 5
- Operation Mode: Background
- Remote Control - Web Browser Access - http://<ipaddress>:8080 : click line. Choose enable for bluetooth (can disable later)
- Shutter Sound: Disabled
Web page is viewable at: http://<ipaddress>:8080 There is an MJPEG stream link near the bottom half of the screen. This stream should be accessible by ZM.
This application records Video to a SD card. Intended to be used as a alternative to Dashcams. You can grab the videos off of the android through ADB or a rooted device. Old videos can be automatically deleted. It is unknown whether videos can be imported into ZM.
By rooting your device you can gain access to full linux arm repositories. It should be possible to stream the camera with popular and well known programs. However, rooting a phone can be difficult. Each android phone has its own quirks to root it, and it is often not worth the time. This is by design, and known as built in obsolecence.
Gives access to debian repositories.
Used on Single Board Computers (such as Beaglebone) for webcam Mjpeg streaming.
In this author's opinion, it's not worth using an Android phone as an IP Camera, when you have other options. You are relegated to wifi only, rooting is difficult, cellphones have privacy issues, and all the free and open source Android applications currently available don't quite work. There are also compatibility issues with some phone models and these programs. Until a compatible and well made FDroid IP Camera program appears available, I'd recommend using an SBC.
In defense of the cellphones, they are cheap, they are plentiful, and they are low power. If you choose one model of cellphone, and are able to gather a significant quantity, learning its quirks in the process, potentially using the play store's IP Camera app, you may have a better experience with these phones.