BT is better than that for the weekend calls as they include 01/02/03 and 0845/0870 at the weekend, and not just 90 minutes free but all calls (up to 60 minutes, hang up and redial to continue) are included.
I'm stuck with BT for a bit (free line installation in return for making 10 calls a month, every month, for 18 months, plus a 50 quid deposit [which they have refunded])... My 10 calls a month were easily used on redial to an 0870 ISP dial-up number (just to be 100% I made 10 calls for the month!) and then I made calls to friends and family (so if I tried someone and got no answer, I would never be hit by a penalty fee by BT).
BT does a line rental discount if you pay for a year in advance [hint: the saving is more than you'd get if you put the same amount of cash in a bank account given current rubbish interest rates].
But with the BT "offer" there is a drawback in that if you change to have calls charged by some other firm, the prepayment is non-refundable... it is their way to reduce people switching to Sky or TalkTalk, I think.
I've seen Primus mentioned with low monthly line rental fee, but I use 1899.com (daytime calls to 01/02/03 can be made to landlines for 5p per call no matter how long, and 10p/min to mobiles, but I don't know if 1899 is blocked by Primus, and if not now, then possibly blocked in future).
Plusnet offers a calls and line rental package from about 12 quid, and broadband on top for another 12 quid (depends where you are living, it can be up to 18 quid in rural areas), I've been with them off and on for last 8 years (gap when I moved and had no landline connected, when I started using Three mobile), and before them tried Eclipse, UKFSN and Freeserve (now Orange) broadband but that is going all the way back to 2001!