We're back from our trip. Thanks for all the help and recommendations on UK Cell Phone Plan options. As I noted earlier in the thread, we went with GiffGaff, specifically a Rolling Monthly Plan. It worked great for our whole trip. It does include some EU roaming in the plan which my daughter will likely use during her travels. MMS (picture texts) being excluded from the plan was a new twist for us. US cell plans include them in the unlimited messaging allotment. This is easily worked around with WhatsApp, InstaGram, etc.

I cancelled the plans for my wife and I for now until we return to Europe in March or April. The fact that we can keep the same UK Phone Number when we return is great. Final note, I was able to purchase the plans, activate them, and activate 5G service from home (United States) before our trip. All in all, I am a very satisfied customer.

--Jon

P.S. I'd gladly accept MMS being an extra charge in the US if our cellular plan rates were similar to UK cellular plan rates. US cell plans are much more expensive.