astf,
Hve a look at regex.split -> http://www.b4x.com/android/help/regularexpressions.html#regex_split`or use the search function - its exactly what you're looking for.
Dim String1 As String
string1 = "3,251,54,874,521,2548"
Dim StringValues() As String
StringValues = Regex.Split(",", String1)
For count = 0 to StringValues.Length -1
' do what you need with each StringValues(count)
Next