C# - Linq - Group By Multiple Tables?

Using Linq to Sql how do i group the following 2 tables.

Orders Table:

CustomerID | Name |Date
1 | order1 | 2010-01-01
2 | order2 | 2010-01-01
2 | order3 | 2010-04-01

Calls Table:

CustomerID | Name |Date
1 | call1 | 2010-01-01
3 | call2 | 2010-06-01
2 | call3 | 2010-05-01

I want to group the two tables by date , Result:

Date | Orders | Calls
2010-01-01 | 2 | 1
2010-04-01 | 1 | 0
2010-05-01 | 0 | 1
2010-06-01 | 0 | 1

i know how to group a single table ,from o in Orders group o by o.Date.Date into og select new {Date = og.Key,Orders= og.Count()};