Looking up Contact from phone number - Old vs New URI: Old fails, New Succeeds?

I've read related several questions here and can't find the answer to this: I have an Android 2.1 device (HTC Incredible). My app, however, must be compatible with early (pre SDK 5) devices, so I am using the deprecated format of filter URI:

Uri contactUri = Uri.withAppendedPath(Contacts.Phones.CONTENT_FILTER_URL, Uri.encode(number));
Cursor C = context.getContentResolver().query(contactUri , null, null, null, null));

The number is of the form 15555551212. This fails to find the Contact, at least on my device. However, changing to the new (SDK 5 and later) ContactsContract format URI

Uri contactUri = Uri.withAppendedPath(ContactsContract.PhoneLookup.CONTENT_FILTER_URI, Uri.encode(number));
Cursor C = context.getContentResolver().query(contactUri , null, null, null, null));

results in success. Originally, the corresponding number in the Contact was in the format +1 555 555 5555, but I changed it to exactly match the开发者_StackOverflow中文版 input number 15555555555 and the old format URI still fails. In both cases, the new format URI succeeds.

Does anyone have any thoughts as to why this is the case? I'm stumped!

That was it. The old API just won't do. Needing to be compatible with older devices, I used Reflection to laod and use the new API calls (ContactsContract) on API > 4.