Using magnets in phone cases?

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I'm going to make a cotton & felt case for my phone later this week and I bought magnets like these (http://www.kleins.co.uk/sew-in---non-visible-power-magnets-1101-p.asp) to use to close the case.

Then I thought... Is it safe to use powerful magnets so close to my phone? Anyone have any experience with this?

Also, patterns for iPhone cases (with or without magnets) would be great. My phone is actually a Motorola Milestone XT720 but it's roughly the size of an iPhone so I'm sure I could modify the pattern...