Giffgaff dont require you to make a chargeable transaction every x number of days.

www.giffgaff.com

Providing you recieve at least 4 mobile calls of 10 seconds or more every 180 days no need to top up further..


Clause 13.3  of the giffgaff Terms & Conditions states:

13.3. Your SIM Card will be disconnected unless, at least once every six months, your Account is used to:
a) make at least one call, SMS or MMS to another number (not including calls to emergency services or Member Services);
b) make at least one connection to the Internet;
c) make at least 4 received calls of more than 10 seconds;
d) make at least one airtime credit or Bundle purchase; or
e) receive Payback Points.