If you want to remember a phone number, more digits of Pi or any other long string of numbers, here are two mnemonic devices to add more meaning to those numbers. They could aid your ability to recall information in a snap.
The simplest method is to memorise a sentence or even a poem. The number of letters in each word represents the digit. For example, as the Mentat Wiki points out, "May I have a large container of coffee?" would represent Pi as 3.1415926. To represent 0, you'd use a 10-character word. Obviously, this would only be useful when you have time to count the letters, but it's still easier to remember a memorable phrase or even a poem than it is to remember a meaningless string of numbers.
Another method, for those musically, inclined is to translate digits as notes and then turning those notes into a song. In a great article about Pi and memorisation, CNN writer Elizabeth Landau says:
When I was a teenager I saw a website suggesting pi could be a song, with one as middle C, two as D, three as E, etc. This helped me get up to 178 digits in college, winning me a T-shirt.
There are a number of other number memorisation techniques, such translating numbers to letters and creating phrases out them and the chunking technique. Find one that works for you and you can start relying more on your own memory rather than having to look things up all the time.