My wife's 2003 XJ8 has its original onboard phone. Verizon advises that in December that phone is no longer compatible because it is 3G and will no longer function.

What is the solution? Is there a dealer upgrade or a replacement phone that will fit the car's mount?

 

in the USA, the 2003 cars were the same generation as the 1998-2002 cars in the rest of the world; the X350 XJ was introduced in the US market in model year 2004/while most of the rest of the world got theirs as an '03.

For the X308 cars like yours, the option that would allow you to keep your current radio would be to install (or have installed) a Bluetooth hands-free kit, such as the Parrot-branded units or one of the old-stock Motorola hands-free kits. I have both brands of units in three of our other cars. Either setup would allow you to continue to have integrated hands-free phone capability by interfacing with your original radio. Otherwise, this would be a really good opportunity to go with an aftermarket radio/head unit that has Bluetooth baked in (that would likely be a substantial upgrade over the original radio). In any case, once carriers switch off 3G service, unfortunately, your current built-in phone will be a relic/paperweight.

To add music streaming capability to the stock radio head unit, the gentleman in the UK who makes the Jagdroid units also has a Bluetooth interface available for the X308 XJ and the XK8.

Best,
Paul