It all depends on your phone. Some phones can upload the entire phonebook in one go, some others can only do one number at a time, while others cannot upload any numbers at all.
for published information from Toyota (other than the section of the Prius Navigation Owner's Manual), see:
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US TSB EL001-05. May 20, 2005 Revision. BLUETOOTH COMPATIBLE CELLULAR PHONES. 2004-2005 Land Cruiser and Prius. (Lists compatible Bluetooth cellular phones, and functions/features/networks/drawbacks by cellular phone model.)
Motorola RAZR Motorola V80 Motorola V500 Motorola V505 Motorola V551 Motorola V600 Motorola V710 Nokia N-Gage Nokia 3600/3650 Nokia 3620/3660 Nokia 6230 Nokia 6260 Nokia 6310i Nokia 6600 Nokia 6620 Nokia 6650 Nokia 6810 Nokia 6820 Nokia 7600 Nokia 7610 Nokia 9810 Panasonic X70 Sharp GX-15 Sharp GX-30 Siemens S55/56 Siemens S65 Siemens SX1 Sony Ericsson K700i Sony Ericsson P800/900 Sony Ericsson T68i Sony Ericsson T610 & T616 Sony Ericsson T630 Sony Ericsson T637 Sony Ericsson Z600
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Nokia 6310i (guide) Sony Ericsson T608/T610 (guide) (older versions of this PDF used to have the Sony Ericsson t68i listed, I think in place of the T608/T610)
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BlackBerry 7100g (guide) BlackBerry 7100t (guide) BlackBerry 7290 (Cingular) (guide) BlackBerry 7290 (T-Mobile) (guide) BlackBerry 7520 (Cingular) (guide) Motorola RAZR (guide) Motorola V330 (guide) Motorola V505 (guide) Motorola V551 (guide) Motorola V600 (guide) Nokia 3600 (guide) Nokia 3620 (guide) Nokia 3650 (guide) Nokia 3660 (guide) Nokia 6230 (guide) Nokia 6600 (guide) Nokia 6620 (guide) Nokia 6820 (guide) Nokia 7610 (guide - coming soon) N-Gage QD (Cingular) (guide) N-Gage QD (T-Mobile) (guide) Siemens S56 (guide) Siemens S66 (guide) Sony Ericsson T608 (guide) Sony Ericsson T610 (guide) Sony Ericsson T616 (guide) Sony Ericsson T637 (guide) Sony Ericsson S710a (guide - coming soon)