O2 is planning a series of promotions to boost sales of the next iPhone in the United Kingdom, according to Macworld UK. Citing unnamed sources, the report states that the device will cost £100 with an 18-month contract, or £269 contract-free for pay-as-you-go users. The new iPhone may be offered free to customers who sign up for the most expensive tariff, which is currently £75 per month, and may be offered as a free upgrade for existing iPhone…