Square and Paypal are two simple payment processing systems that we at CPI have used successfully and can recommend.
Square works with your iPhone, Android phone, iPad, or even iPod. It is also possible to process a payment through the Square website. The fees are reasonable and best of all the money is usually transferred to your account by the next day.
Square will mail you their free nifty credit card reader so you can swipe cards anywhere. It is a great way to collect payments from your doula or birth business clients. And at a flat fee of 2.75%, Square is well below other payment systems. If you sign up now then you can process up to $1,000 in credit card sales for free during the first 180 days.
You can also take payments through your website with Square or Paypal. They offer pay now buttons or a shopping cart you can embed onto your website to receive payments. Invoices can be emailed with a payment link so that processing payments is extra simple.