To enter the information in your TaxAct® return when another individual (other than your spouse if filing a joint return) received a Form 1098 Mortgage Interest Statement for interest you also were liable for:
Once the previous steps are completed, when you print the return you will see the "See Attached" text to the right of the amount on Line 10 on Schedule A (Form 1040) and a sheet will print with the return titled "Additional Mortgage Interest Information" which is the statement required by the IRS.
Per IRS Publication 936 Home Mortgage Interest Deduction, on page 9:
More than one borrower. If you and at least one other person (other than your spouse if you file a joint return) were liable for and paid interest on a mortgage that was for your home, and the other person received a Form 1098 showing the interest that was paid during the year, attach a statement to your paper return explaining this. Show how much of the interest each of you paid, and give the name and address of the person who received the form. Deduct your share of the interest on Schedule A (Form 1040), line 8b, and print “See attached” next to the line. Also, deduct your share of any qualified mortgage insurance premiums on Schedule A (Form 1040), line 8d.
Similarly, if you're the payer of record on a mortgage on which there are other borrowers entitled to a deduction for the interest shown on the Form 1098 you received, deduct only your share of the interest on Schedule A (Form 1040), line 8a. Let each of the other borrowers know what his or her share is.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.