don’t forget you can’t stick to old phones for long as with each year 3gpp improves air interface features on the 4g lte protocol stack. before going to 5g you should get some pre-5g performance feature enhancements on cat 6.9 chipsets. for example, lte used to be on single and independent rf carriers but now can carrier aggregate and offer better forward error correction and interference mitigation algorithms. moreover, old frequencies are refarmed from 2g and 3g and repurposed for 4g, thus those old phones that run only 2g and 3g chipsets may be made obsolete and cannot run on all bands anymore. by then you’ll be left high and dry as they keep warning you about turning in your very old phones for new ones. for me i’m looking forward to 6.9 by 6.9 mimo tx and rx features which will offer me streaming video services while on the move. 4g lte will reach 64x64 mimo (although i prefer 69x69) while 5g will offer 256x256 mimo on the get go.