If you want to accept Credit Cards info over the phone, you will need either PayPal's Virtual Terminal which costs $30 a month plus transaction fees or you can use PayPal Here and input as Card not Present. Note, fees are higher when you process as card not present.
As for sending an email invoice, all you need is their email address. Note, you will need either a Premier or Business account, you can't accept credit card payments with a Personal Account.
