<p>as google does not deliver what i want to know, i try to ask stackoverflow :)
what is the number of max concurrent connections to a sql ce 3.5 database?
thanks
j.</p>

I believe the information you are looking for is the SQL Server Edition Comparison.
For standard Editions -
Compare Features
For Compact Edition -
Compare Features
Edit
Sorry, this
Word Document
is most likely what you need.
Edit again
The answer is 256 concurrent connections for Compact, unlimited for express.  See table 1 in the linked word doc.