moving over to php 5

Hi, It is about time I made the jump to 5, however the only thing that is holding me back is the problem with hosts. How many hosts still run php 4 and am I going to have to spend hours and hours persuading them to upgrade before I can run my code? I have very little time as it is and am anxious that this is going to be swallowed up on the phone to hosing companies and their rubbish technical staff. Please let me know if I will find this an easy transition or should I hold off for now. R.