Micro SD's are compatible with the following phones:

BenQ-Siemens: CF61, CL71, EF81, EF91, EL71, P51, S68, S88
E-TEN: M600
Hewlett Packard: hw6500, hw6900
HTC: MTeoR, TyTN
i-mate: JAM, JAMin, JASJAR, PDA2, PDA2K, Smartflip
LG: P7200, U300, U400, U8290, U8360, U8380, U880, U890
Mio: A701
Motorola: A1000, A780, A920, A925, C975, C980, E1000, E1070, E398, E770v, MPx, MPx200, ROKR E1, SLVR L7, V1050, V360, V3i, V3x, V635, V975, V980
Nokia: 3250, 5500, 6125, 6131, 6136, 6151, 6233, 6234, E50
O2: XDA, XDA Exec, XDA II, XDA IIi, XDA IIs, XM
Orange: M1000, M1500, M2000, M500, M5000, SPV, SPV E100, SPV E200, SPV M600, Treo 600
Palm: Treo 650, Treo 700
Qtek: 2020i, 8500, 9000, 9090, 9600, S100, S110, S200
Sagem: myS-7, myV76, myX6-2
Samsung: D600, D820, D830, D900, E770, E870, E900, i300, i300x, S500i, SGH X700, SGH Z500, Z130, Z300, Z400, ZM60, ZV40
Sanyo: S750, S750i
Sendo: X
Sharp: 770SH, 802, 902, GX30, GX30i
T-Mobile: MDA Compact, MDA Compact II, MDA III, MDA Pro
Vodafone: VPA Compact