Are you allowed to use a cellphone while driving as long as there isn't any oncoming traffic?

No, using a cellphone while driving is generally not allowed, regardless of traffic conditions. Most jurisdictions have laws prohibiting the use of handheld devices while driving to ensure the safety of all road users. Even without oncoming traffic, distractions can impair a driver's ability to react promptly to unexpected situations. It's always best to pull over safely if you need to use your phone.