How many songs can iphone 4 hold?

I think it's about 1,000 songs. It all depends on the firmware you have installed. Firmware 1.1.* will hold more than 2.* due to the simple fact that as firmware is updated, more storage is needed for the OS it self. Its like Windows. XP only required about 1.5GB and now Vista is pushing 10GB more functionality = less free space for you.