Fields filter

hello everybody.
how can i do some filter in custom fields on order page? i have a "telephone" field, and can i protect this field from invalid input(letters)?
very very sorry for my bad english

How can I replace this standard telephone field from address table to order table?

Hi,

Are you using the Address step in the checkout ?
If yes, why don't use the normal phone field of the address, because you find it in the checkout as the order custom fields.

To have a secured phone in the order table, it require custom code.

I'm don't use adress step. Can you say me, how I need modernize code?

You can edit the view "checkout / custom_fields" and check if the custom field is "telephone" so add the JavaScript on fly check on the field to display.

oh, i think it's too difficult for me(( can you tell me step to step about this?