If your MAGI is $110K or more then it depends whether the "Retirement Plan" box is checked on either of your W2's. If it's checked on either one or both of your W2's you may not deduct the IRA contribution as the phase-out of deduction ends at $110K for couples who file as Married Filing Jointly. If it is not checked on both W2's you may take the IRA deduction.
From page 12 of IRS Pub 590
www.irs.gov/pub/irs-pdf/p590.pdf -
"the deduction you can take for contributions made to your traditional IRA depends on whether you or your spouse was covered for any part of the year [emphasis mine]
by an employer retirement plan. ...if either you or your spouse was covered by an employer retirement plan, you may be entitled to only a partial (reduced) deduction or no deduction at all, depending on your income and filing status."