Does the Apple iPhone 5 use the 700 mHz band? Might it interfere with wireless mics that operate in the 700 mHz band?
Yes. Information on Apple's website indiactes that iPhone 5 can use the 700 MHz band for LTE data. In the U.S., wireless mic systems have been banned from using 698 - 806 MHz starting July 1, 2010. If wireless mic systems in this frequency range are in use (as of September 2012), the iPhone5 will likely cause significant interference.
The iPhone5 model A1428 (sold by AT&T in the U.S., and Rogers, Bell, and Telus in Canada) uses 734-746 MHz (TV 58-59) and 704-716 MHz (TV 53-54). The latter range overlaps discontinued Shure wireless systems that employed the UB-band (698 - 716 MHz.)
The iPhone5 model A1429 (sold by Verizon and Sprint in the U.S.) uses 746-756 MHz (TV 60-61) and 777-787 MHz (TV 65-66). The latter range overlaps discontinued Shure wireless systems that employed the UA-band (782 - 806 MHz.)