Yes. €20 top up gets unlimited* internet, free weekend texts to any number and free Three to Three calls, I think. The €20 isn't taken for any of that so remains available for chargeable calls. I'm switching back to Tesco Mobile soon, I only switched to Three because Flag Driver didn't work on Tesco Mobile back then, not sure if it does now but, to be fair, it's shite regardless.
*subject to fair usage, terms and conditions, etc..