> when I send texts from my mobile, I couldn't care less whether 3G or GSM is used. A phone I purchased almost 4 years ago could do both automagically.
Yes, the same way you can use IPv4 on top of either wired ethernet (802.3) or wireless (802.11). A laptop purchased more than 4 years ago could do both automagically.
What we are talking about is more like changing the phone number format or the SMS packet format, not switching between technologies lower in the stack (3G/GSM and 802.3/802.11 are all link-level), so your analogy is a red herring. Changing the link (which affects only that link) is a local decision, and thus much easier than changing a higher-level protocol (which affects everyone).