I use a re-fill sim card that I got for free in the mail many years ago.
I could change the kind of price plan/charge every time I need to add credit to the sim card, no bills, no period of notice, and I can just log in to my internet bank and charge my sim from there if it depletes. Thing is I'm at home a lot and use wifi, and I don't really do social calls a lot.
Personally pay 7,5 Euros monthly for and that's what I get to call and text for. Included in the price mentioned is also 200MB of data for surfing. If I'd not use all of the data, or all of the credit and fill the sim card it would of course keep the credit and data I have and just add onto it. All and all I have 1.38 GB of Data on my phone right now out of all those 200MB re-fills.
However, if I knew that I'd need to use my phone a lot, I could just pay around 20 Euros to the same carrier and get unlimited free calls, unlimited texts and 10GB of data valid for 30 days(pretty similar to a subscription but without needing any paperwork), and once past those 30 days it would go back to my old credit c:!