I was on the original TalkTalk tariff, which was introduced when TalkTalk launched many years ago. That tariff included unlimited broadband, unlimited phone calls to 01, 02 & 03 numbers (but not 0845 or 0870) and unlimited telephone calls to most EEC countries, USA, Canada, Australia and New Zealand).
I make very few international calls and I realised that other ISPs were advertising cheaper tariffs. However, my TalkTalk broadband service was fast and reliable - and I didn't want the hassle of switching. I discovered that I could halve the cost by changing to the following TalkTalk tariff:
Simply broadband £3.50 per month
Anytime UK call boost £5.00 per month (includes unlimited calls to 01, 02, 03, 0845 and 0870 numbers)
Total £8.50 per month
Although I have a direct debit arrangement, I obtain a 15% discount for immediate payment by credit or debit card upon receipt of each bill, which reduces the cost to £7.22 per month.
I use the 1899 service, if I need to make an occasional international call. However, TalkTalk do offer various boosts that include international calls, which might be attractive to anyone who makes a lot of international calls.
I also pay my line rental annually in advance. The annual TalkTalk line rental cost £126 in December 2013 (equivalent to £10.50 per month). That was cheaper than any other provider. It is probably more expensive now, so check the cost. You can switch to annual line rental at any time, even midway through your contract.
I arranged everything through the TalkTalk sales number, and did not need to speak to their retentions department.