This is up to your programmers. If they don't know, they are confused. The programmers decide what type of compression is acceptable and you decide within that compression what the sample rate will be.
- WAV is never used by a sane person in IPhones because of their uncompressed size. Though it is never in a final game, some programmers will compress themselves so this is a possible format.
- MP3 is a likely candidate if they are ok with slightly larger files than what is possible but require instant loading of music. So no runtime decompressing is allowed.
- OGG is what I prefer but it has some overhead if you want to decompress it on load. A lot of IPhone developers will prefer this because a general goal is to get your file size under 20MB if possible. In my case, 18 of that is reserved for everything besides music. The problem with OGG is the decompression time can take a little bit. So for this you generally have a MP3 file of a short loop to play until the main loop is decompressed.
All of these possibilities require some knowledge of audio on their parts. If they don't understand that, it's your job unfortunately to explain the differences. Otherwise, give them a lossless clip and have them figure it out.
Keep in mind a lot of audio software adds gaps on purpose. These gaps are to zero out the wave on the clip. If you had the amplitude at anything over zero when your clip starts, the speakers will pop. Sometimes the software overcompensates and adds an unloopable gap. Open the clip in a raw wave editor like audacity and cut out the extra space and make sure you still start and end at zero amplitude.