The 18th is just the deadline for the $100 Amazon gift card when buying a new phone. There has been no date set yet for when the old plan/system will be shut down. So you have time yet on the old plan.
From my research, talking to Motorola customer service the phones that are sold by Visible are made for them to work on the Visible network. If you buy an unlocked Motorola phone from somewhere else including Motorola even though Visible sells the model the model number itself is different. Other than being sold by Visible it is highly doubtful that it will pass the IMEI checker. I bought a 2021 G Power from Visible and of course the new plans rolled out and that is not compatible. Picked up a new 2022 G Power and got a card for it and stuck it in the 2021 model and activated it and it worked without issue. I could not say for sure if your G7 will work or not.
Here's some information about Motorola, their phones only get one OS update and 2 years of security updates which means even though my 2021 model worked fine it will no longer get updates and 2022 version I just got has used it's one OS upgrade to 12 when 13 is already out and 14 will be out this year sometime and I will only get another year of security updates. I even asked Motorola why they don't upgrade them longer like their competitors, their response word for word "we can't upgrade them forever". With that said when I need my next phone I am looking at Pixel not only because they have a better update policy and from me checking used Pixel 6A, 7 and 7 Pro on eBay the unlocked ones I found that listed IMEI numbers everyone passed the checker. This tells me they are not restricted like Motorola phones are. In a year or two I will look at Google's lower cost phone, kind of like what the 6A is now.
