Solar sunroof messing with mobile and GPS?
 

Ever since getting my 97 D2 I've struggled with getting decent phone reception and get almost no satnav gps reception. I put it down to a kind of 'Faraday's cage' type effect of that enormous spool of wire in the roof which is the solar sunroof. Given the solar panel doesn't appear to do anything anyhow is it possible to replace this with normal glass? Was there a straight glass version of the sunroof made? Has anyone else had similar problems?

Yep. Same with me and I don't have a sunroof. It's the athermic (metal) coating in the twin pane windows, which I'm guessing from your issue, is what your car will be fitted with.
On my last 8 I had a sunroof, which I opened when I needed to improve reception. A pane, but it worked ;)

Do you mean OEM car phone and GPS or standalone aftermarket items, if latter then it's most likely that you have heat reflecting window glass. I had all windows like that in mine and aftermarket GPS would not get any signal in car, did not notice any issues with phone. I since have replaced front windscreen with regular as it had lot of small chips and scratches and I sourced new one cheaply. Since then there are no problems with GPS reception. Changing solar sunroof for glass might improve it but I don't know by how much. In my opinion solar sunroof is one of the best features (after V8) and I would never change it for regular glass.

It'll be dead zones in the windscreen - try mounting your nav in different places and see if it improves it. There's usually spots around the rear view mirror for toll charge units to sit and get clear reception. Renault's are similarly afflicted. Later '8s don't have the same kind of metallized glass