Not with a Siemens, but we looked into it once with a France Telecom machine and after discussing w/both vendors engineers it was decided E1-Q.Sig (ISO) was the way to go.
Works good, we're getting full integration transparency both ways, MWI set/clear, CFB/CFNA reason codes, name/nbr, divert, step-back on busy, etc.
Only problem I've seen is man-busying individual trunks or even the whole span on either end is not reflected across the link unless you knock down the D channel, but I think that's pretty typical with Q.Sig PRI.
We're also doing Q.Sig between a SX2K and a Cisco CM; not as robust, but name/nbr and MWI stuff works OK.
Same probs w/busyout.
Ditto Q.Sig to a Northern M1, again not as robust as with the France Telecom system, but at least name & number is getting passed both ways.
Your mileage may vary..