I was able to finally get an answer from the dealer. I figured I'd post
this info in case anyone else has had this problem. The release of the
button immediately after the warning triangle lights was the key to my
finally being able to reset this. From my sales guy:

O.K., the 2003 and 2004 instructions are the same, however, according
to one of our Senior Volvo Techs, the process takes practice. It
appears timing of when buttons are released is critical and a bit
tricky. Here's the process:

1) Turn key until just odometer is displayed; you do not want to see
the various warning lights that display with a bit further turn.

2) Select trip odometer 2.

3) Hold trip odometer 2 button in while turning key to activate bank of
warning lights.

4) Watch for orange warning triangle in center of instrument panel
display to flash once and release trip odometer button immediately.
Continuing to hold trip odometer button or having the warning light
remain lit will not reset Service Warning. This takes practice
according to Jonathan, so if the first try doesn't do it, try again
from the beginning.

I was able to finally get an answer from the dealer. I figured I'd post
this info in case anyone else has had this problem. The release of the
button immediately after the warning triangle lights was the key to my
finally being able to reset this. From my sales guy:

O.K., the 2003 and 2004 instructions are the same, however, according
to one of our Senior Volvo Techs, the process takes practice. It
appears timing of when buttons are released is critical and a bit
tricky. Here's the process:

1) Turn key until just odometer is displayed; you do not want to see
the various warning lights that display with a bit further turn.

2) Select trip odometer 2.

3) Hold trip odometer 2 button in while turning key to activate bank of
warning lights.

4) Watch for orange warning triangle in center of instrument panel
display to flash once and release trip odometer button immediately.
Continuing to hold trip odometer button or having the warning light
remain lit will not reset Service Warning. This takes practice
according to Jonathan, so if the first try doesn't do it, try again
from the beginning.