It is dependent on the hardware. If your phone does not support LTE, you will only be able to use 3G.

Most phone manufactured in recent years had the hardware to VoLTE capability. However, the device must be tested and approved by Koodo before VoLTE can be used. If you are looking for a VoLTE phone with Koodo, check this link https://www.koodomobile.com/en/help/volte?srsltid=AfmBOoq1UiVJtpfry4zQZoj0sCJmc_6gf8GLrFrkI14RcNw88ytzWnrv

and I don’t recommend you “hack” your phone. It might create many other security issue

To add to Dinh, the reason why a lot of older devices aren’t supported by newer software is because the hardware of the device simply can’t handle it. You will find that it will run the software quite slow due to a weak processor, possibly over heat, or the battery dying quite quickly as it will put a lot of strain on the device to run the software and more if the update you install is much further ahead than what the device is compatable with.
 

I’d go with their recommendation and just simply purchase a newer device as it can cause more problems than fix them with the forced update alternative, that or come to terms with the 3G price increase if it is an older device that doesn’t support VoLTE.

I'd like to thank all of you for all the VERY useful information.   Definitely clears things up for me.  Couldn’t find a definitive answer elsewhere online.  Some said yes, some said no. 

And Dinh, as far as not hacking my phone, well, I understand the possible security concerns.  I did  root my previous phone (Galaxy S3) and had no issues at all.   But I have to add that I never engage in any activities  that would cause me any security problems on a phone -- no banking or financial transactions of any kind, no gaming, no visiting questionable sites.   

In fact, I almost NEVER access the ‘net on a phone.  It’s only when absolutely necessary. 

I use the phone 99.9% of the time simply as a phone --- for making calls, texting, and watching an occasional Youtube video.   If I’m going to do any real work or banking or problem-solving research, I do it on my desktop machine that has a nice 23” monitor that doesn’t make me squint. 

Thanks again, all;  even though this info is not what I hoped to hear. 

Back in December I upgraded from the S3 to a used S5 Neo and just now found out that it can’t do VoLTE.  Unfortunately,  despite Koodo’s year-long texting barrage warning me I needed to upgrade, they did NOT warn me of this VoLTE requirement.   So I spent the money on a  this newer phone and now I find it’s going to become a high-tech paperweight.  And it’s too late to get a refund on it.

*SIGH*  

In the old day, rooting was exciting as it allowed many extra capabilities and unlocking. However, in recent years, I noticed that there was a hardly a compelling reason to root anymore.

Koodo  provided VoLTE function on their network if customer is using S10 or newer. The S5 Neo wasn’t on their VoLTE list ever. https://www.koodomobile.com/en/help/volte Additionally Canadian carriers are phasing out 3G network, it is just a matter of time. Soon, every phone in Canada will need to suport VoLTE.

     >The S5 Neo wasn’t on their VoLTE list ever. 

Uh-huh … as I said earlier, it would have been nice if they had included that information when telling me I needed to upgrade.

     >Soon, every phone in Canada will need to suport VoLTE.

Could you please tell me HOW soon?  I’m wondering if I should just wait and pay the extra $3.00/month for now.  But if 3G is going to be shut down as soon as the new year, I might as well upgrade immediately. 

3G has already been shutdown in the US.  But in Canada no government sunset date has been assigned so it is determined by the individual carriers for now.

Here is what's known about 3G sunsets in Canada:

• Rogers: March 31, 2025
• TELUS: no fixed date. Speculation from various sources say end of 2025. 
• Bell: no fixed date; probably similar to TELUS.

https://forums.redflagdeals.com/canadian-3g-shutdown-sunset-timelines-2700838/

Thanks, Dennis.  It’s funny; that link is the exact same page that I was looking at just before I posted the question.    Guess we’re all going to be in the dark regarding the shutdown until they finally decide.

I was hoping maybe Koodo/Telus might give me a direct answer themselves.  Oh well.