How do I: Ericsson T29S prevent from roaming?

Have you tried setting it to "manual search" mode? This forces it to stick with your chosen network until it's not available, and it then gives you the option to search for another network.
Failing that, I think you can delete networks from the 'preferred networks' list. It's been a while since I used Ericsson phones though, so you'd best check the manual. You should be able to d/l one from the website.

re

glue it down

I'm sure the Rabbit has a few Swedish or Danish instructional videos he can lend you..

One of my coleagues has an Ericsson T29S. He lives near Elsinor in Denmark and when at home the blessed machine keeps roaming to a Swedish network, consequently running up big bills.

He can tell the phone to "prefer TDC" but it only last about 1/2 hour before it is back on a Swedish network.

When he wants to make a call it is OK to set the "prefer TDC", but when he is receiving a call it is not possible to see which network the phone is on, so can't answer for fear of it being on roaming and hence charging him for the call.

I've suggested that one can remove the Swedish operators from the SIM, I used to do this myself on my old phone as there was an expensive French and a hopeless Belgian one I didn't like to use, but can't remember what I did and it was a completely different type of phone anywhere.

Any ideas, or instructional videos?