My problem:

Table: **trans\_detail**:

```
PhoneNo | Datetime
01234   |  2013-01-05 20:40:10
01245   |  2013-04-02 21:00:13
05678   |  2013-04-16 01:24:07
04567   |  2013-07-23 07:00:00
etc     |  etc

```

I want to get all `phoneNo` that appears at least once for every month in the last X month (X month can be any month between 1-12). 

For example: get all phone no. that appears at least once for Every Month in the last 3 months. 

I am using SQL Server 2005.