Wrong phone number format = issues when sent to Paypal

By default, Zen Cart accepts most any possible phone number format the user decides to enter when creating their account.

This didn't seem to be an issue until I configured and tested Paypal Payments Standard module. The module works perfectly ...except that when a user and their order is forwarded to Paypal for checkout, the passed value for the Phone field is mangled as Paypal accepts only the first 10 digits.

Thus a user who has entered something like: 1-803-123-4567 as their phone number end up with 180-312-3456 when reaching the paypal checkout screen. Clearly most users should spot the error ...but if not, and they fail to correct this, the result is likely to be a failed Paypal transaction due to mismatched data.

Is there a built in way to restrict a user's phone number entry? If not, how do other Zen shop owners deal with this? :huh:

I can forsee customers entering a myriad of formats when signing up ....but then later having issues during checkout.