I have 3 out of 4 Uniden GMR5089 radios.
Can I replace the missing one with any 2 way radio, or do I need another GMR5089?
I want to communicate between all 4 radios. I take them camping with my kids.
The GMR5089 is an FRS/GMRS radio, so it should be compatible with most other consumer FRS/GMRS radios currently on the market.
One the premise that you are in the US, there are really only two compatibility issues that you may encounter with using FRS/GMRS radios from two different manufacturers. It is possible that one manufacturer will assign the frequencies to different channels from the other manufacturer. It doesn’t happen a lot, but if it does, it’s still not a big deal since there are only 22 total FRS and GMRS simplex frequencies available, so it’s simply a matter of determining which channel each one is programmed into. The manufacturer will generally print a table of these channel and frequency assignments in the user manual.
The other possible issue is the assignment of “privacy” codes or “interference eliminator” codes, also known as CTCSS and DCS codes. Each manufacturer has their own set of code assignments, and the number of codes available to the user can even vary depending on the model. The easiest way around that is to simply clear all of the codes from the radios, then try to match them up by cross referencing the CTCSS/DCS tables in the user manual for each model.
There may be a feature disparity that might be an issue, such as one radio may have call tones or some other shared feature that another radio may not support, but these are relatively minor things.
Here are some resources that may help.
Video Radio 101 - The facts about GMRS two way radio compatibility
Article Radio Compatibility: Which Models Will Work Together
Video Radio 101 - Privacy Code Issues on GMRS Radios
Podcast TWRS-08 - Talking Publicly About Privacy Codes
Forum Discussion setting up privacy codes