Per FAR 12.204(a): "The contracting officer shall use the Standard Form 1449, Solicitation/Contract/Order for Commercial Items, if (1) the acquisition is expected to exceed the simplified acquisition threshold; (2) a paper solicitation or contract is being issued; and (3) procedures at 12.603 are not being used. Use of the SF 1449 is nonmandatory but encouraged for commercial acquisitions not exceeding the simplified acquisition threshold."  In other words, you can use the DD Form 1155 if the procurement is within the $250,000 simplified acquisition threshold. If the value is above $250,000, you should use the SF 1149...even when using simplified acquisition procedures iaw FAR subpart 13.5 (Simplified Procedures for Certain Commercial Items).