If you pay in advance at AT&T with a credit card, overage charges are the same as buying a second plan for 250MB for $14.99, or 2GB for $25.
If you pay after exceeding your data plan limits (on your AT&T phone bill), the overage for the smallest plan is an additional $14.99 for another 250MB, but only $10 per 1GB of overage on the 2GB plan.
Verizon offers four tiers of service: $20 per month for 1GB, $35 for 3GB, $50 for 5GB, and $80 for 10GB.
Verizon's overage charges are $20 for 1GB over its entry-level 1GB plan for $20, but those purchasing 3GB or more are charged $10 per 1GB of overage.
Can't decide between 3G data plans? Experts said that the added two tiers of service on Verizon's data network might entice heavier users, particularly those with gaming and video needs. On the other hand, tethering at AT&T with the iPad 2 and similar overage charges at Verizon for the biggest data plans could favor AT&T.
Some experts suggested using the carrier you trust and have experience with. Your assessment could include how good the 3G services have been on both carriers, and also how you have been treated when it comes to repairs and billing.
And many customers will exclude the carriers' 3G networks from consideration altogether, experts noted, sticking with the Wi-Fi-only version. As Wi-Fi has grown more widely available, it has become a viable option for many users, analysts and others noted.
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