Can one device do everything?

Sometimes it is cost effective to have more than one device.  This depends on your specific requirements and often the schools policy towards mobile phones.  

For example.

If it is important to take a photograph of the board, or create reminders......  and a student is able to use their phone then the device does not need to carry out these functions.

If audio recording is important consider buying a digital voice recorder. While most phones have voice recording facility they take up a lot of valuable space.  Once a phone is full it is no longer helpful.

Buying multiple devices is sometimes more cost effective than
buying one high end computer that can do everything.

With both audio and photographs you need to establish an efficeint workflow that ensures all these files are easily transferred to the students device.